Seen with primitive boolean action parameters:
It seems the internal model representation is 3-state, while the rendered representation is 2-state.
There seem multiple issues:
1) An initially checked checkbox leading to a validation failure, that clears the checkbox, then after checking the checkbox via user interaction, validation passes.
2) Validation fails on a parameter (complaining that it is mandatory), while the domain logic states that any of the 2 possible states (false/true) are valid.