I noticed one of my files always reverted some positioning. I then played around and noticed, that if you crop a symbol its position is not restored correctly after a reload. (OS X Yosemite, Mockups 3.1.7)
So what I do:
- I insert a symbol at coordinates 100, 100 (x,y)
- I select the symbol and crop it, I cut off the top 100px, so the new coordinates of the cropped symbol are 100,200
- Then I move the symbol up to the old coordinates 100,100.
- I close the file
- I reopen it.
- The symbol then us at coordinates 100,200 instead of 100,100.
If you make a group around the symbold and crop that instead it works fine.