1. click pan crop on element (image) in timeline.
2. checked Mask on element's timeline
3. used pen tool to make a quick mask
4. clicked on pan/crop layer of time line and put a keyframe down-stream somewhere
5. clicked on that keyframe (just to be certain)
6. adjusted the size of my element
7. made sure mask keyframe timeline has only that first keyframe.
The mask still adjusts in proportion to the size of the element.
If I am understanding this,, you have a picture and you mask say an inch in diameter , you the zoom in on the picture and the masks grows in porportion to the picture ?
do you mean that you are trying to zoom in on a portion of the image and have it masked all the while the same size?
then I would suggest taking 2 tracks, making a white mask in the parent track make the track of video a "child" track to the parent mask track, setting the parent track to "multiply mask" will be necessary. Then you can zoom and crop the picture in the video track as much as you want and the mask shape/size won't change.
I was fishing around and figured it was going to be a parent/child thing. That's a relatively new area in my Vegas experience...I haven't needed it until now.