I was having issues with this three column, full screen, multi-row layout when I set each image at 100%. It seemed to be fine for about 10-15 seconds, then there was a “shift” in everything and everything reset so there was a space between each column/row.
Thanks for posting about this – definitely sounds odd.
I did some testing but wasn’t able to see or reproduce the issue. If you are seeing other behavior on your end, can you send me a screen recording of what you see (CloudApp or Quicktime work well)?