I may have run into the same bug.....
When you create a memblock from an image its directly related to what bit mode your graphics mode is running in.
EG.
i made a memblock from an image in 16bit .... and the memblock bytes returned is in correct.
The only way to fix the command is to make sure your running in 32bit mode.
can be tested with this command if you have the plugin it came from
bitmode=display depth()
if bitmode<>32 then message "kill the app and prompt the user to change graphics modes":end
edit:may not be the same problem your having.... but is one that i have noticed