session.merge fails since [5961]

**Migrated issue, originally created by Anonymous**

session.merge fails for PickleTypes since [5961](5961), I attached a test file (needs werkzeug from werkzeug.pocoo.org to put the object into a cache) and the output.

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Attachments: [log](../wiki/imported_issue_attachments/1426/log) | [test.py](../wiki/imported_issue_attachments/1426/test.py)

