Great suggestion. Thank you.Alinta commented
I'm using the iPad app and have the same problem. Since we all know by now Microsoft isn't reading this and does not care to help I thought I'd share something I found.
Go to the upload list, press and hold the file until it turns grey, keep holding and slide it to the left to bring up the delete file upload option. It will remove it completely from your upload list.
You have to delete them one at a time, no bulk delete option. Not fun when there's 350 files to manually delete. Cheers MS.