I have the same problem and this is huge. You can apply a mask and feather a clip, but if you then crop it to allow for a soft blend between the connected clip and the clip on the main storyline, you LOSE THE FEATHER. This really sucks. The feather does not change to the new cropped clip but IT SHOULD.
To fix this problem Apple needs to add feather back to the crop tool like it did on every other version of FCP known to mankind.