This is a followup to
my post a few days ago about inadvertant opacity envelop pull-down by 1-2%.
Here's another way to inadvertantly create an opacity pull-down:
Position the cursor on the time line. Mute or solo the video track. Use the left or right arrow key to move the cursor. The cursor won't move, because the Video Track Header is the active element on screen. But, since the Track Header is active, and only the opacity slider can move, you will have altered the opacity of the entire track.
It's very easy to do accidently, as I discovered. Make checking for opacity envelopes a "must do" before rendering your projects!
Jack