The list of allowed characters currently includes: 023456789ABCDEFGHJKLMNOPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz$-_.!
I suggest removing !.- from that list, because they can cause link trail problems in some software.
! and . have link trail breakage problems in Thunderbird, and in plain wikitext links
- has the problem in just Thunderbird.
(Possibly other software platforms are also affected. Those are the examples I know of.)