Focusing screens MX <-> LX

[Gonz]

In the MX focusing screens manual, it says that MX focusing screens can 
be used in the LX.

In the LX focusing screens manual, it says that LX focusing screens are 
exclusively for the LX.

Does that mean that LX focusing screens cannot be used on the MX, but 
the converse can?

Has anyone ever tried to put an LX screen into an MX?
Thanks,
rg