Have you ever get a problem like this?

if it happens with non-alpha meshes then
maybe the non-alpha mesh is being
obscured by an alpha mesh or, if that
is not likely, then the engine "thinks"
that the non-alpha is an alpha mesh.

maybe because an alpha mesh is
setting a non-alpha mesh to alpha.

btw, could you do us a favor and see if the
"flicker-points" are still there in the other
blitz versions from 1.86 to 1.90?

that is, if you don't mind. thx.