In 4.06 --keep-locs became a default in the compiler driver. This means that the various foreign.mli files compiled and installed no longer sport the same digest (I do think that the wrong thing is being digested here but that's another question).

The fix should be to simply compile the various foreign.mli with the --no-keep-locs option. I think this is the problem witnessed in dbuenzli/tsdl#44