I don't think it's a bug, more of an oversight imo. Here are the screenshots
This little constant can't be parametarized in the blueprint
[boskid] Decider combinator output constant is not parameterizable
Re: Decider combinator output constant is not parameterizable
I am hestitating here a lot because i know blueprint parametrisation collapses all the numbers intentionally so they can be changed all at the same time and this means by adding another parameter that by default has a value of 1 will often join other parameters in blueprints. Given that this only affects blueprint parametrisation i decided to add ability to parametrise this output constant (only when it is selected) for 2.0.43. That seems to be consistent with the overall goal of blueprint parametrisation and in worst case it will break some existing blueprints with parametrisation by including previously not covered value when applying parameters.