Adding effects to a clip seems to remove a line of pixels at the edge.

Hi, new here. I have looked around the forum but can not find a similar post or answer.

Issue:

In a timeline I place an interview clip.
Then I place other clips over the top of the interview - 2nd angle or B-Roll - whatever.
Then when I add the letterbox filter* OR a color filter to the top clip I get about one pixel border of the top clip disappearing to reveal the clip underneath. This seems to be with most filters, letterbox, vignette, color finale. Please see screen shots.
*If I've added the letter box to the top clip I also add to the bottom clip

There are work arounds, but its just more work and rendering.

In the screen shots I've added you can see I've added a custom generator as the upper most clip to create letterboxing which has "fixed" the horizontal pixels but the vertical are still present.

Work arounds:
I can toggle the clip underneath off, but I have to cut each clip either side and then if you want to change something later you are dealing with many clips not one.
I can also increase the scale of top clip by .5% but then this effects letterboxing / is just another thing to render out.

My system set up:

OSX Yosemite
Version 10.10.5
MacBookPro (Retina, 15 inch, Mid 2014)
Processor 2.8GHz Intel Core i7
Memory 16GB 1600 MHz DDR3
Graphics NVDIA GeForce GT 750M 2048MB

FCPX 10.2.2

Footage from Canon DLSR and Sony FS5 both behave in the same way.

Has anyone else experienced this? Did you find a way to fix it? Any advice or input would be gratefully received.
Thanks!
JJ