Sony Vegas - black borders

[Ratchet]

Hello.
When I uploaded my videos on youtube I went to the "video manager" and then I saw that on the thumbnails are some black bars on top, bottom and right side.
I always rendering my videos in 1920x1080 16:9 and I didn't have this kind of problem yet.
Do you have any experience with this problem and Do you know how to fix that ?
(I know that I can upload my own thumbnails but I trying to find the cause of this, whether it's happening only to me or also to other people.)
Thanks.

[Rainbow]

Had this before when editing Vinyl. I remember it was the input files that fucked me over (prerecorded xbox footage). Never had the same problems with Fraps. No idea why it happened though and the effect was always random between clips, but consistent on the same clip (importing multiple times).

What I did to solve it (labour intensive way): pan&crop every single clip on which it happens.
Short way (doesn't work often): uncheck the maintain aspect ratio box.

[Ratchet]

Tried both solutions but it didn't help. Black bars are still there.
Can't be something wrong with youtube ?
 
When I uploaded video in July this year, I didn't have any problem with that but if I upload video now, with same render settings, it's already fucked.
Also when I'm looking in my Google profile on the thumbnails of videos which I uploaded 6 months ago, there are those black bars which wasn't there before.

[MaCi]

It's probably some shit with Youtube because I've been getting those borders too with videos containg nothing but a white background.

[PM]

I have it on all of my videos' thumbnails too.

While the borders aren't on the actual video.

[VaNilla]

Workaround: Upload a custom thumbnail .

[Rainbow]

Tried both solutions but it didn't help. Black bars are still there.
Can't be something wrong with youtube ?

That's because I thought the problem was not only on the thumbnails but also on the video  This is probably a youtube issue.