Does anyone know how seriously Fannie Mae enforces anti-flip clauses and how it discovers violations of anti-flipping clauses? 

I remember when i first started practicing real estate in CA.   There were no issues, what these institutions try to do is stop deep pocket investors from gobbling up all the deals.   The priority, or so they want, is the primary home owner.   What i later found is that if you don't abide by these rules would be in big trouble

Simple to monitor.  The deed transfers are recorded, and easily viewable, forever.  Simple solution though...you can transfer immediately for less than the 120% cap (perhaps to your other entity?).  the new deed holder has NO deed restrictions, and can immediately sell for whatever.

@Wayne Brooks   Thanks for the information.

My question is not whether Fannie Mae can discover the transfer easily but whether it seriously enforces anti-flipping clauses.

Moreover, my understanding is that the anti-flipping clause is contractual and does not affect the deed.

It is generally a deed restriction, contained in the deed, if the closing agent doesn't screw up and leave it out.  I a assume enforcement.

Just doubled checked. Looks like the deed is restricted. Thanks!