This has been reported in TWiki:Support.SID-02397
: With recent Perl versions, there are still some not-yet-fixed occurrences of unescaped left braces in regular expressions.
I could reproduce the behaviour. The syntax check doesn't capture the problem because the regular expression is built at runtime, and it hits only under certain conditions which aren't easily available for the current automated test (but well described in TWiki:Support.SID-02397
). Up to Perl 5.29.10 this is a warning
and not an error, so I'm not sure why and how this effects the WYSIWYG editor.