Status: Fixed for next update.
I've reuploaded the set of default images, with the fixed menu font, too. Please do not include this fixed version in your pack if the only thing you want is the font fixed; just wait for the next update where the default will be fixed. However, if you're wanting to use it as a start point for custom fonts, go ahead. :)
The platformer now displays for 7 frames an additional brick just above the correct position. See attached image.
PS: If you are already fixing the images, you might as well have a look at the little "x" in the font for the preview screen/result screen. It has on the left side a small blue vertical line. The platformer sprites are much more important though.
Re: Platformer, I'll get that fixed. I notice even more problems when using NXPs rather than single files, too (affecting other skills that display bricks, as well as destruction particles - basically, the bricks / particles don't appear at all). When playing single levels, it would appear only the Platformer is affected, and only when the non-Santa lemmings are in use.
Re: Font, yes, there's a few (less significant) problems with other characters too, IIRC. This is something I need to go over at some point.
EDIT: Got all those fixed. The platformer brick positioning was a mistake in the graphics file; the rest of the issues relating to bricks / particles were a bug in the code.