Custom instructions disrupting GPT-4 reasoning?

Can someone provide an explanation (and perhaps a solution) for this please?

I use the following prompt:

“I’m in my house. On top of my chair in the living room is a coffee cup. Inside the coffee cup is a thimble. Inside the thimble is a single diamond. I move the chair to my bedroom. Then I put the coffee cup on the bed. Then I turn the cup upside down. Then I return it to rightside-up, and place the coffee cup on the kitchen counter. Where is my diamond?”

I ask GPT-4, without a custom instruction, and it responds correctly:


I ask GPT-4, with a custom instruction, and it responds incorrectly (it responds as if it were GPT-3.5 that was responding):

The custom instruction is simply:

“My name is Jon.”


I ask GPT-4, again, without a custom instruction, and it responds correctly:


Thank you.

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