https://bugs.winehq.org/show_bug.cgi?id=11770
--- Comment #28 from Austin English austinenglish@gmail.com --- (In reply to Alistair Leslie-Hughes from comment #27)
I can confirm this works with Advanced SystemCare (bug 40534), which tries to attach its bug report to an email to send to its support team. Without the patch it opens thunderbird with a subject/to, but no attachments. With it, my bug report and screenshot are attached.
@Austin, does Jeremy's patch from #c23 fix the problem?
Yep, both Jeremy and Mark's patches fix attaching files to a Thunderbird draft.