Fish-Eye warp gets parts of picture outside of mask
I have a peculiar problem. It seems like even though I have created a mask, where I expect my warped picture to be inside - I get some weird parts that are coming outside of the mask.
I have first created a plane in one color.
On top of this one another plane in a different color with a mask so I get to see the plane below.
On top of this second plane I have a picture (doesn't matter if it is a video). This picture I have created a fish-eye warp effect to. Then re-sized it to about 12% and placed it on top of the area where I have the mask in the second plane. A mask is then drawn with the Freehand tool.
I then expect that the picture should be within my mask, but possibly due to the Fish-eye warp some parts end up outside.
The example here is quite basic. I first encountered it when masking out a rear view mirror in a car shot on a green screen in order to simulate that the mirror showed the traffic in the rear.
Any ideas on why this is happening? And how do I post a picture that illustrates the issue?