I have run into this issue every once in a long while; it happened again today so I thought I would post about it and see if it was just me. Since it is so rare it is difficult to track down a cause. I only have some limited evidence to go on - but have demonstrated the issue, on my system, with multiple files, even after closing FMP.
The problem is that when I manually type in a value (Height in this case) for the Body layout part (although, I have seen this happen with the Footer as well), the new Height I just typed is NOT the resulting Height - the layout part resizes to some drastically different dimension. E.g. if I type in 29, the Body part resizes to 113. Here are some screen shots from today's episode. I had noticed the Body was an odd fractional size, so I was just going to move it to 28. I entered that number and hit return - that number is what appears in the Inspector field, but the Body element resized to 133 instead. #1 is the 'before' - odd fractional dimension (not sure how it got that way). The 2nd screenshot demonstrates that I have typed in the value and moved out of the Height field - it is showing the "28" value I typed, but the erroneous result is shown in the layout part. #3 shows what the new value is that it came up with.
The exact numbers aren't particular; after it started behaving like this, I could type in 15, 20, 18, 24, 50... and it would stay at 133. I could type in larger numbers (e.g. 200) and the element would grow; but returning it to 28 only brought it back down to the bogus size of 133.
Shutting down FM and restarting it didn't help, either. This one file still does it - maybe it's more repeatable than I had thought, and I just only run across it very rarely. I tested another layout in this same file and it was also doing the same thing, but at different numbers. I tried another file that I had open at this time and it didn't behave oddly on the Body element, but it DID happen in the Footer. It appears to be whatever the Layout Part that is at the bottom; e.g. there's no Footer below the Body in my original case. But if I add a Trailing GS to this layout, the Body now becomes functional - it doesn't oddly resize. But the Trailing GS DOES erroneously resize. So it appears to be restricted to whatever the lowest Layout Part is. I tested this in a separate (hosted) file and it is also demonstrating the problem - whatever element is at the bottom.
I don't have any stray objects in the gutter that are extending down - when I do "cmd-A" to select all, the outer bounding box encompasses only what's plainly visible on the layout. There are 4 points of space between the bottom of the lowest Body layout object and the bottom of the Body element itself.
* OSX 10.11.6
* FMPA 15.01
* FMPA 14.05
* Local and Hosted files
* Happened on a co-worker's computer, too (the same Hosted file as I was testing with).
* Unable to reproduce on a new file; the 2 files I have seen this on, however, are utterly unrelated - i.e. they aren't branches of some original file, where not made on the same system, don't have code or layouts copied between them.
Has anyone else run into this? I did some searching but didn't come across anything. Since it seems rather repeatable, I'd figure I wasn't the first one to come across this.