I think we get seduced into supposing that the *minds* of F1 and F2 are identical, even though they are material instantiated in different substrates, because we imagine that they have similar content and thus identical properties. However, this is too hasty. The mind of F2 might have all the same prior content (e.g., memories, supposing flies have memories); however, the mind of F2 has *new* and *different* content that the mind of F1 lacks: namely, whatever it (F2) is presently experiencing. Since the mind of F1 and the mind of F2 have different properties, they are non-identical.

(This reasoning raises all sorts of problems with traditional beliefs in reincarnation and resurrection!)