Handle backslash in escape function.

Fixes: #4595.

Candidate for stable

src/support/lstrings.cpp

@@ -1179,7 +1179,8 @@ docstring const escape(docstring const & lab)
 	for (size_t i = 0; i < lab.length(); ++i) {
 		char_type c = lab[i];
 		if (c >= 128 || c == '=' || c == '%' || c == '#' || c == '$'
-		    || c == '}' || c == '{' || c == ']' || c == '[' || c == '&') {
+		    || c == '}' || c == '{' || c == ']' || c == '[' || c == '&'
+		    || c == '\\') {
 			// Although char_type is a 32 bit type we know that
 			// UCS4 occupies only 21 bits, so we don't need to
 			// encode bigger values. Test for 2^24 because we

status.22x

@@ -125,6 +125,8 @@ What's new
 - Protect citation arguments (pre and post text) which contain brackets
   (part of bug 2751).
 
+- Handle backslash in label and ref insets (bug 4595).
+
 
 * LYX2LYX