I've an idea then where things may be going wrong. When you're editing a post it's temporarily saved, then when finally posted it transfers everything over. It sounds like it's this part which is faulty.
I agree on everyones points with uploads. I keep procrastinating about fixing it as I know it's such a troublesome feature to code up and have working reliably x-browser/x-app, also what happens with unused uploads (need deleting after a while), file formats that are acceptable, re-sizing hi-res images if needed to reduce file size, reading exif data and rotating upside down pictures, having a working progress bar for uploads so people don't give up, what happens if files get corrupted. Then shifting files around... well not too bad but adding drag and drop is complex, desktops need mouse down, mouse move and mouse up events, mobile users need touch start, touch move and touch end events and thumbnails need to snap and shuffle around similar to moving phone app icons. It's complex!
I'm tempted to remove the upload window mind, agree there is no need to pull images from google photos / dropbox etc. Anyone use that feature at all? If using the mobile app it's often a built in feature now to pick photos from other services on your phone directly.
The other thing I'd quite like to do is change the media viewer. On desktops it's ok (except arrow keys to toggle through), but on mobile it often shows the image smaller and doesn't allow for zooming in which is sometimes annoying.
All on the to-do list. Perhaps something for my next holiday.