Pinned VACB may be flushed twice

Since the implementation of the lazy writer, once a BCB is marked dirty, and thus the VACB it refers to, the VACB may be flushed at anytime on the disk. Even if the BCB is still pinned.
If that happens, the VACB is marked clean.
On unpinning, given the BCB is marked dirty, the VACB is marked dirty again and flushed again, whereas it had no changes.