That is not a change, but how Migration always worked. It was never possible for more then one pop to migrate away from a planet at any given time.Which implies the patchnote was supposed to limit arriving migrants.
Which seems to not work at all.Which is just another case of 'did noone in QA consider actually TESTING THAT CHANGE'.
Ah, did not notice that before. In that case this is a clear case of bug report.
EDIT: been too long away from forums. Do not have access to forum areas where game specific bug reports should be filed...