When you insert a Frame Member with Frame Generator, by default, the Part Number is in sync with Content Center since the "Get Frame Member's Part Number from Content Center" box is checked by default.
If you want the pre-2011 behavior back, please uncheck the "Get Frame Member's Part Number from Content Center" box.
When this box is unchecked, the Filename and Part Number are identical.
When this box is checked Content Center determines the Part Number and the Part Number will no longer be in sync with the Filename.
The state of the checkbox is remembered for the next insertions in the same Inventor session.