This issue is also mentioned in some of the comments from the tail of
#13839 [1,2,3].  Victor even quoted the XTerm changelog :p.  I don't
see a patch for this particular issue in #13839, although Stefan posts
a patch for some other keymap stuff, and Victor floats an alternate
regexp [1].

[1]: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=13839#11
[2]: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=13839#14
[3]: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=13839#17