This is a known issue that will be addressed in an upcoming release later this year.

i''ve also encountered this problem, and to me it seems to be a realy annoying bug. i''ve tried using the array as pointer, while taking into accont the pitch; it didn''t seem to help, but here is the important part:

int stride = back.SurfaceDescription.Pitch;
byte[,] barr = back.LockMicrosoft.DirectX.DirectDraw.LockFlags.SurfaceMemoryPointer );
unsafe
{
fixed (byte* pbdata = barr)
{
for (int j=0; j<100; j++)
{
for (int i=0; i<100; i++)
{
*(pbdata+j*stride+2*i+1) = 0xF8;
}
}
}
}
back.Unlock(barr);

i''m using a 16bit rgb device and this code should paint the surface red (its a 100X100 backbuffer surface called back).

however, it paints half the surface. i''ll be happy to know if this code works for u, and what am i doing wrong