Not quite sure if outright bug or missing functionality, but feels broken: currently, it seems impossible to set the default value for a parameterized constant to any value used elsewhere in the blueprint without causing those other instances of the value to also become parameterized.
For example, consider the following setup:
Let's say I want to set the default value for the parameter 0 in the constant combinator to 1:
As soon as I apply this change, that parameterized value is force-merged with the constant 1 in the other two combinators, effectively breaking the blueprint: