Field Parameter grouping breaks in Matrix visual

Hi,

Having some difficulty with using a Field Parameter in a matrix; it looks like there are some similar issues out there so this one is possibly a bug, or I'm missing something obvious.

Example data used due to confidentiality; hopefully makes sense from a high-level.

I have the below field parameter:

{
	("Measure 1", NAMEOF(MasterQuery[M_Measure1]), 1, "Headline", "Section 1")
	, ("Measure 2", NAMEOF(MasterQuery[M_Measure2]), 1, "Headline", "Section 1")
	, ("Measure 3", NAMEOF(MasterQuery[M_Measure3]), 1, "Change", "Section 2")
	, ("Measure 4", NAMEOF(MasterQuery[M_Measure4]), 1, "Headline", "Section 3")
}

When I add this to a matrix, I want to group my values by the 4th column (Section 1/2/3), but what happens is, the grouping doesn't apply, and all measures show under all headers. I've tried to illustrate this below where you can see the behaviour vs. the expected:

I've also tried creating a dimension table based on the unique values and using that in a relationship but it returns the same behaviour which seems even more odd.

If I filter by the column this works as expected which is why I'm suspecting a bug.

Anyone else encounter this/have any suggestions?