This bug is present in both 12.13-RC and SLX, reporting it here because it'll need to be fixed for both.
The problem lies in the SavePngStream method in PngInterface.Pas - it's one of the methods Anders updated, seemingly making use of an updated PNGWriter.
Best guess: old PNG-saving code needs to be updated. Investigating, I'll post here if I manage to find a fix.
