> The issue is that the engine does not fully resolve the SELECT before starting to perform the INSERT operations. So the SELECT starts to see the new records which have been inserted by the current statement... and so the statement runs without end.

FB missed feature which is usually called "cursor stability".
Actually, the behaviour in this case isn't that simple and INSERT SELECT
doesn't always fall into endless loop. It depends on select's plan. If
the plan includes SORT - no endless loop.

SY, SD.