I don't understand. Wood frames and wood don't have the same specs (AFAIK, didn't check), and neither have cobble and concrete the same specs (very very sure of that). If you upgrade from cobble to concrete the weight of that block definitely changes
If you meant that the collapse happened between two blocks of the same weight, that isn't a surprise either, one was probably slightly nearer to his nearest support and therefore had just enough support and the other didn't. Also collapses often don't happen at the block which is out of support but on blocks that are part of the "support chain".