When holding a step, multiple destination steps may be pressed sequentially to make multiple copies of the source step.
While holding a pattern, only the first destination pattern becomes a copy of the source pattern. Subsequent presses of other patterns simply ignores the held source pattern and instead just selects the last pressed pattern as the active pattern.
In the absence of a pattern block Copy (which would be a HUUUGE improvement), being able to make multiple copies of the same pattern, without having to hold the source pattern again for each operation, would streamline the workflow.
This seems like a bug as I can’t see a reason for this inconsistent implementation.