Hi 

I replaced a sub-assembly within an assembly and updated / repaired all the mates and saved the file.

When I close and reopen the master assembly I can see the new sub-assembly in the preview however after it rebuilds it reverts to the old sub-assembly. So I closed the master assembly again (without saving) and moved the old parts/sub-assembly to another directory so it won't be able to reference it. But when I reopen the master assembly it still is referencing the old part/sub-assembly.

It should not be possible - it must be referencing a part in a temporary memory somewhere. 

Very very frustrating.