In every version of Premiere in the last 2 years (14.6 currently) there is the same problem on every workstation:
When fading in or out a masked layer (subsequence or title) in the first frame the whole mask is black (not transparent as it's supposed to be in the first frame of a fading) and fades then to the opaque picture (from black).
As Ann notes, unpacked a bit, this forum's design is screwy. So please drag/drop the images or clip into your text reply area so it appears directly in your post and others don't have to download strange files to their computer in order to help.
In trying to figure out from your comment what you're doing (and not particularly sure I have it correctly in mind) ... I can't say I've ever seen this behavior.