I regularly make backgrounds for PowerPoint, both in 4:3 and 16:9 depending on the screen in the room where I will be using PP.
In Magix P&GD (18) I set the page size to 16x9cm or 16x12 (for 4:3) and design my background. As per usual, I "store" elements I am not using in the grey area's not on the page. Sometimes the background is just a bit bigger than the page or imported png's or jpg's are not completely on the page (on purpose). When I export to JPG I choose the Page option (so that only what is actually on the page is exported) and 100 DPI.
When I use these backgrounds in PP, they are never quite the right size (proportion); there is always a small white margin on at least one side, usually on two, sometimes three sides. I have to manually adjust (stretch) the image by -0,1% or -0,2%. This is a pain.

My question is: why is a 4:3 (or 16:9) page size in P&GD not actually that propotion upon export? Or is this a (known) PP problem and not P&GD's problem at all? Or am I doing this wrong?

David