Not unusual..... I hope you meant AM/FM CASSETTE with C.D.:There is very minamal room for the Tape, let alone the Adapter with the wire. If you try to Force the Adapter, you may actually bend the Mechanism.Also, some Tape Decks have Sensors on the Take Up Reels that require a Pull on the other Take Up Reel to let the Tape Player know there is a Tape in the Mechanism. If it does NOT Sense the Pull then it will try to Auto Reverse &/Or Eject.
Your best bet would be to get a FM Modulator that plugs into the Cigarette Lighter & your I-Pod. Sold at most 12 Volt Shops & Wal-Mart. This way it would work in virtually any Vehicle with a AM/FM Radio.....& will not cause problems with Tape Deck