Using with batch inserts/updates causes memory leak

[er1z]

Q	A
Bug report?	yes
Feature request?	no
BC Break report?	no

Steps to reproduce:

1. Create a console application with thousands of inserts/updates, preferable with any progress bar,
2. Observe that IOPS amount per second is dropping as the import goes by.

I'll post a PR with fix in a couple of moments because it required some digging.

[er1z]

@beberlei, any news?