Kelkschiz
YTtalk Mad
Hey man heres a fix, follow these steps and it'll work!
1) Go to "edit" on your video.
2) Upload the custom thumbnail.
3) Hit "SAVE CHANGES"
NOW IS THE IMPORTANT PART
4) Go to "Enhancements" at the top, next to "info and settings"
5) Hit "Save"
This for some reason gets around the bug!
Let me know you how get on!
When you do that, will it actually try to 'improve' the video as well?