When trying to add characters that are in violation of the $wgLegalTitleChars the program doesn't error out or skip the input gracefully, but instead crashes and doesn't provide meaningful output.
Common error:
[XDmdMwNiX64pb2H-OgFOtQAAAAk] /wiki/Special:ImportUsers Error from line 129 of /home/xxxx/public_html/w/extensions/ImportUsers/ImportUsers_body.php: Call to a member function setEmail() on boolean