Reply 80 of 99, by 640K!enough
I have been having recurring problems with file attachments when composing private messages. There seem to be two different, but related problems, so I'll go over both.
At first, when trying to attach a file, it was treated differently if I dragged the file onto the message window, or tried to click "Add files" and use the file selector. The former worked, while the latter displayed a message that only one attachment is permitted, even though it was the only attachment, and my first attempt at adding a file. After that, Submit/Preview/etc. were all disabled, with a "tool tip" of "Still uploading file" (or similar), yet it had already failed and there was no network activity. There were no options to cancel or delete the attachment. It was stuck in a state that prevented re-trying. The only apparent way out was to load a different page. This seems to have been mostly fixed.
The newer problem shows the same symptoms if an upload fails, for some reason. It shows "HTTP error", then gets stuck in that same unusable state. For the sake of completeness, all of the files in question were less than 50 KiB.