Currently, the extension uses this regex:
$re = '~<tvar\|([^>]+)>(.*?)</>~u';
when parsing the content of "tvar"[1], but this does not work if the content spans multiple lines, as in
https://www.mediawiki.org/w/index.php?title=Thumbnail_style_update&diff=1074482&oldid=1074458
I believe it would work if we set PCRE_DOTALL for this regex (if that is the case, this is an easy bug to fix, so I'm adding the appropriated keyword to the bug report).