I have made a fix for this in the mapeditor now.
It worked for me when I did some quick testing.
So please give it a go and let me know how it goes.
It should allow 5 extra characters now --> !.,:- <--
As usual since this is a fix on already running code, you must reload the cache-files.
In Firefox an F5 (when mapeditor is loaded) is usual enough.
In Chrome you need to go and select delete offline cache.