Images move when using presentation mode in Impress

I add a main PNG image (a logo) then line up some other smaller PNGs into a precise arrangement.
When I select to present the slide show (F5 or Shft F5), both the presentation screen and control screen show the PNGs have moved position by several mm relative to each other. This spoils the desired arrangement.
Apart from the images there is nothing else on the slide and no animations have yet been added.
When i come out of presentation mode the images are back in the correct place.
I can’t lock them in a group as I want to animate them individually.
Any ideas?
I’ve tried with jpeg images and the same thing happens.

Your LO version? Your OS? Upload sample file?