Jens said to write this into a thread on it's own as I found it earlier today and had mentioned it in a different thread, so here goes in case it's worthy of investigation at some point...
I was playing about with the overscan and resolutions on my A1200 which is fitted with an Indivision AGA Mk3 to see if either made any difference to some flickering I was experiencing (it didn't seem to), and I noticed that if I set the overscan to greater than 704 pixels in DblPAL progressive and laced, and then move the pointer sprite to the far right of the screen, the pointer sprite doubles in height. The same also seems to happen in DblNTSC prog and interlaced too. I don't have an analogue multisync monitor to check if the Amiga's normal video out does the same thing.
Hope this is useful, cheers!