Know this discussion is almost a year old..
I have exacctly the same problem, when rendering a .mp4 H264, using the Vimeo Preset in Adobe Media Encoder CS6 from a QT AppleProRes that has no issues itself.
No problems occur when rendering a Quicktime .mov with H264 Codec (No Vimeo Preset)
i used white text on solid black. After compression it appears as grey backgroung, white text and same black mist in the lower right corner as shown on post 1
I've been searching around in the internet for a while, but couldn't find out, if you know please share, thanks!