With 3.12. build an attachment dragged to new message windows must be dropped to attachment tab. In previous version it was enough to drop attachment anywhere in the message text area. It is uncomfortable and probably unintended regression.
Changes related to this bug have been committed. Please check latest Git and update the bug accordingly. You can also get the patch from: http://git.claws-mail.org/ ++ ChangeLog 2015-07-25 14:04:02.042213608 +0200 http://git.claws-mail.org/?p=claws.git;a=commitdiff;h=6f576ea745340829c3aa6ac412db497e68ca0c95 Merge: b017736 3b14f47 Author: Colin Leroy <colin@colino.net> Date: Sat Jul 25 14:04:01 2015 +0200 Merge branch 'master' of file:///home/git/claws http://git.claws-mail.org/?p=claws.git;a=commitdiff;h=3b14f476066860518abe501187f600125832f2ad Author: Andrej Kacian <ticho@claws-mail.org> Date: Sat Jul 25 14:02:33 2015 +0200 Fixed handling of drag&drop onto compose text area on Windows. Fixes bug #3475.
Good catch, thanks! The drag&drop semantics have changed slightly in recent versions of GTK+ for Windows. The fix will be included in next Windows release (coming soon-ish, depending on few more bugfixes).