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I was working on a project when a custom block started behaving unexpectedly. I copied the project and deleted everything except the custom block and it still behaves weirdly. I've added a new custom block and that is behaving normally… see https://scratch.mit.edu/projects/361247932/

I have not seen the input value for a boolean evaluated as 1 before like in your example project.

Did you ever delete inputs that were earlier than the boolean inputs from the custom block as this sometimes causes problems.
(although this should not produce a 1).

I can't remember exactly how I managed this and I haven't been able to replicate it. I did make several changes to the block on several different occasions. One thing that may be important is that the original block was almost certainly made in 2.0…