Sorry, perhaps one thing I didn't mention
: I'm not using Auto snap mode, but instead I activate Center mode before selecting.
In fact with Autosnap I can replicate J-J behaviour; instead, using Center snap, I have some drawings which snap to centers and some which doesn't.
With Center snap active, in the last example file I've no problem to snap to circles' center from outside blocks; all entities are recognized to my QCad with this drawing. This does not happen with the first drawing, in which I can't.
So I'm speaking of selecting centers when Qcad is in SnapCenter mode. It's not a bad matter in fact if, with Auto snap mode, block reference points and line ends (rightly) have precedence over (and therefore do mask) centers.
So, in short, my initial problem still remains:
I have 2 drawings: in the 1st I can't snap centers inside blocks (in Center snap mode) whereas in the 2nd drawing I can do it; the 2 drawings have different behaviour and I can't guess which is the difference between them. If I cut+paste the problematic block in a new drawing the problem disappears: so it's a problem specific to the drawing (which in fact comes from outside cad).
As a user it's not a big deal (keyboard BD, slect block and then snap to center, then keyboard EM: and I'm still into my main command with my center selected!).
Sorry for taking it long: I really know it's not a big problem for a designer, but I'm developing a mechanism simulation application in which selections will be 80% arc centers inside blocks and I solving this problem would dramaticaly speed up the user interaction. Also I feel (having drawings without this problem) that likely there is a solution.