Tranform matrix + repeat attribute

[Buola Buola]

I am having some strange problems when using a transformation matrix
on a source picture which has the repeat attribute set to True. It
doesn't map the points in the right place. Has anyone experienced a
similar problem? if not, I will have to do a more detailed description
of the problem and some code which exposes it.
If it helps, I am using xorg 6.8.99.5 and the nvidia closed-source drivers

Thanks for your help,

    xavi