vncviewer 4.0 on XP, problems with cursor positioning from server side

[Michael Russe]

Hi, I wrote my own rfb server for an application which does not use X nor
Windows. I am testing against the latest download from realvnc.com. Everything
works great until I need to set the cursor position on the client side from my
server. I am doing this by sending a 5x5 rectangle with a 5 byte mask with
encoding set to 0xffffff11 as part of an answer to a framebuffer update
request. The viewer will paint some strange patterns around the cursor
position and crash so bad that MS wants to know about it.
Can anybody give me a hint what might be going on and what to change ?
Thanks, Michael