I have figured a temporary solution to this until WordPress can hopefully fix the bug.
Many it seem have been having difficulty seeing the Gallery tab after adding an image to a post and only seeing the 'From Computer, From URL, Media Library' tabs.
My way around this was by first creating a title for my post then saving as a draft. After it has saved and a permalink appears for your post goto 'add an image'. Select the images and upload them. Then click on 'Save All Changes', then the gallery tab should appear with the images you have uploaded.
It seems that a post needs a permalink before it can have items added to the gallery.
This is just my workaround at the moment but you still may have difficulties if you have plugins that are causing the trouble instead, which my advice would be to disable all your plugins, retry this method and reactivate your plugins one by one to find the offender.
Best Regards,
Tim