[xwiki-users] how to debug a picture not being scaled down?

Hello fellow XWikiers, I now have an XWiki 5.0.3 and an XWiki 5.1 where my picture never gets downsized. e.g. /xwiki/bin/download/XWiki/polx/photo%2Dpasseport%2DPaul%2D2012%2D07.jpg?width=50&height=50&keepAspectRatio=true has width 345 x 443 (the original). How can I debug this? The log does not seem to say and it seems not related to have an AWT thread at hand (the 5.1 is run with a graphics environment). thanks in advance. Paul