Comment # 5 on bug 1121221 from Neil Brown

I'm fairly sure that subtree_check is actually irrelevant.  It has very little
real effect and that does not vary between versions.
I suspect that the difference that you thought was due to subtree_check was
actually due to some other (possibly subtle) difference.
But if the problem doesn't appear when you use no_subtree_check, I do find it
hard to motivate further exploration.

The slow mounting sounds most like a network timeout.  This could be caused by
a firewall or by some service not running that should be.  I cannot think of
anything that would affect 4.x, x>0 only though.  In terms of network
connections, 4.1 is simpler than 4.0, with less room for failure.

Sorry that this isn't very helpful.