(reported by hewiki user)
note: hewiki is on 1.34.0-wmf.17 (rMW09c09890d4dd), a day ahead of most other wikis.
- make sure your beta preferences on hewiki do not activate "2017 source editor", aka "New wikitext mode"
- open random page on hewiki. add "uselang=en" to title if you can't read hebrew
- click "edit source"
- click "add media" button (aka "embedded file")
- enter file name and caption
- click "Insert"
the text [[File:aa.jpg|thumb|bb]] is inserted in edit window in caret location
no new text is added to edit window
(i verified on enwiki and arwiki [another RTL wiki]) and both work, but then again, both are on 1.34.0-wmf.16 while hewiki is on 1.34.0-wmf.17)