diff --git a/src/frontends/qt4/GuiTabular.cpp b/src/frontends/qt4/GuiTabular.cpp
index 63cd3836c0..e4719d170b 100644
--- a/src/frontends/qt4/GuiTabular.cpp
+++ b/src/frontends/qt4/GuiTabular.cpp
@@ -47,7 +47,8 @@ namespace frontend {
 
 GuiTabular::GuiTabular(QWidget * parent)
 	: InsetParamsWidget(parent), firstheader_suppressable_(false),
-	  lastfooter_suppressable_(false)
+	  lastfooter_suppressable_(false), orig_leftborder_(GuiSetBorder::LINE_UNDEF),
+	  orig_rightborder_(GuiSetBorder::LINE_UNDEF)
 
 {
 	setupUi(this);
@@ -79,9 +80,9 @@ GuiTabular::GuiTabular(QWidget * parent)
 	connect(interlinespaceUnitLC, SIGNAL(selectionChanged(lyx::Length::UNIT)),
 		this, SLOT(checkEnabled()));
 	connect(booktabsRB, SIGNAL(clicked(bool)),
-		this, SLOT(checkEnabled()));
+		this, SLOT(booktabs_toggled(bool)));
 	connect(borderDefaultRB, SIGNAL(clicked(bool)),
-		this, SLOT(checkEnabled()));
+		this, SLOT(nonbooktabs_toggled(bool)));
 	connect(borderSetPB, SIGNAL(clicked()),
 		this, SLOT(borderSet_clicked()));
 	connect(borderUnsetPB, SIGNAL(clicked()),
@@ -365,6 +366,25 @@ void GuiTabular::borderUnset_clicked()
 }
 
 
+void GuiTabular::booktabs_toggled(bool const check)
+{
+	// when switching from formal, restore the left/right lines
+	if (!check) {
+		borders->setLeft(orig_leftborder_);
+		borders->setRight(orig_rightborder_);
+	}
+	// repaint the setborder widget
+	borders->update();
+	checkEnabled();
+}
+
+
+void GuiTabular::nonbooktabs_toggled(bool const check)
+{
+	booktabs_toggled(!check);
+}
+
+
 static void setParam(string & param_str, Tabular::Feature f, string const & arg = string())
 {
 	param_str += ' ';
@@ -769,7 +789,7 @@ void GuiTabular::paramsToDialog(Inset const * inset)
 	}
 
 	// In what follows, we check the borders of all selected cells,
-	// and if there are diverging settings, we use the LINE_UNDECIDED
+	// and if there are diverging settings, we use the LINE_UNDEF
 	// border status.
 	GuiSetBorder::BorderState lt = GuiSetBorder::LINE_UNDEF;
 	GuiSetBorder::BorderState lb = GuiSetBorder::LINE_UNDEF;
@@ -793,12 +813,18 @@ void GuiTabular::paramsToDialog(Inset const * inset)
 				lb = borderState(lb, tabular.bottomLine(cc));
 				ll = borderState(ll, tabular.leftLine(cc));
 				lr = borderState(lr, tabular.rightLine(cc));
+				// store left/right borders for the case of formal/nonformal switch
+				orig_leftborder_ = borderState(ll, tabular.leftLine(cc, true));
+				orig_rightborder_ = borderState(lr, tabular.rightLine(cc, true));
 			}
 	} else {
 		lt = tabular.topLine(cell) ? GuiSetBorder::LINE_SET : GuiSetBorder::LINE_UNSET;
 		lb = tabular.bottomLine(cell) ? GuiSetBorder::LINE_SET : GuiSetBorder::LINE_UNSET;
 		ll = tabular.leftLine(cell) ? GuiSetBorder::LINE_SET : GuiSetBorder::LINE_UNSET;
 		lr = tabular.rightLine(cell) ? GuiSetBorder::LINE_SET : GuiSetBorder::LINE_UNSET;
+		// store left/right borders for the case of formal/nonformal switch
+		orig_leftborder_ = tabular.leftLine(cell, true) ? GuiSetBorder::LINE_SET : GuiSetBorder::LINE_UNSET;
+		orig_rightborder_ = tabular.rightLine(cell, true) ? GuiSetBorder::LINE_SET : GuiSetBorder::LINE_UNSET;
 	}
 	borders->setTop(lt);
 	borders->setBottom(lb);
diff --git a/src/frontends/qt4/GuiTabular.h b/src/frontends/qt4/GuiTabular.h
index 2cba4810aa..f56abdacfb 100644
--- a/src/frontends/qt4/GuiTabular.h
+++ b/src/frontends/qt4/GuiTabular.h
@@ -33,6 +33,8 @@ private Q_SLOTS:
 	void checkEnabled();
 	void borderSet_clicked();
 	void borderUnset_clicked();
+	void booktabs_toggled(bool const check);
+	void nonbooktabs_toggled(bool const check);
 	void on_topspaceCO_activated(int index);
 	void on_bottomspaceCO_activated(int index);
 	void on_interlinespaceCO_activated(int index);
@@ -67,6 +69,10 @@ private:
 	bool firstheader_suppressable_;
 	///
 	bool lastfooter_suppressable_;
+	///
+	GuiSetBorder::BorderState orig_leftborder_;
+	///
+	GuiSetBorder::BorderState orig_rightborder_;
 };
 
 } // namespace frontend
diff --git a/src/insets/InsetTabular.cpp b/src/insets/InsetTabular.cpp
index f9a78e1d6b..375d7561b6 100644
--- a/src/insets/InsetTabular.cpp
+++ b/src/insets/InsetTabular.cpp
@@ -956,17 +956,17 @@ bool Tabular::bottomLine(idx_type const cell) const
 }
 
 
-bool Tabular::leftLine(idx_type cell) const
+bool Tabular::leftLine(idx_type cell, bool const ignore_bt) const
 {
-	if (use_booktabs)
+	if (use_booktabs && !ignore_bt)
 		return false;
 	return cellInfo(cell).left_line;
 }
 
 
-bool Tabular::rightLine(idx_type cell) const
+bool Tabular::rightLine(idx_type cell, bool const ignore_bt) const
 {
-	if (use_booktabs)
+	if (use_booktabs && !ignore_bt)
 		return false;
 	return cellInfo(cell).right_line;
 }
diff --git a/src/insets/InsetTabular.h b/src/insets/InsetTabular.h
index 1a8bf33243..ddb02763fc 100644
--- a/src/insets/InsetTabular.h
+++ b/src/insets/InsetTabular.h
@@ -402,9 +402,13 @@ public:
 	/// Returns true if there is a topline, returns false if not
 	bool bottomLine(idx_type cell) const;
 	/// Returns true if there is a topline, returns false if not
-	bool leftLine(idx_type cell) const;
+	/// If \p ignore_bt is true, we return the state as if booktabs was
+	/// not used
+	bool leftLine(idx_type cell, bool const ignore_bt = false) const;
 	/// Returns true if there is a topline, returns false if not
-	bool rightLine(idx_type cell) const;
+	/// If \p ignore_bt is true, we return the state as if booktabs was
+	/// not used
+	bool rightLine(idx_type cell, bool const ignore_bt = false) const;
 
 	/// return space occupied by the second horizontal line and
 	/// interline space above row \p row in pixels
diff --git a/status.23x b/status.23x
index edfeea5175..7a75ce55e7 100644
--- a/status.23x
+++ b/status.23x
@@ -178,6 +178,8 @@ What's new
 
 - Fix display of formal table bottom line with multirows (bug 11445).
 
+- Fix left/right border UI when toggling formal table style (bug 9835).
+
 
 * INTERNALS