That's not a bug, it's a feature. ;-)
More seriously, it's a design decision. The benefit of exactly correct
micro bookkeeping does not seem to warrant the extra cost in terms of cpu
cycles spent in the accounting code.
IIRC there was a patch for that some years ago, if you are interested I
will try to find it. No idea how much work it would be to port it to
current kernels, though.
Tim
-