Dear all,

I am hitting a weird problem with the slideshow option for the desktop background. It seems like the current picture is placed on top of the previous one.
This is of course not noticeable when using pictures with the same size, or when scaling.
But if one has "Scaling, keep proportions" and projects a mix of 16:9 and 4:3 pictures, it is clear that two pics are always shown, the latest one just put on top of the previous one.

Reproducible: Always

Steps to Reproduce:
1. set desktop background to slideshow, "Scaling, keep proportions"
2. choose a set of pictures with different aspect ratios
3. let the slideshow run

Actual Results:  
current picture is overlayed to previous one

Expected Results:  
current picture should replace the previous one