Ok Toni, thanks.
What surprised me is that this "feature" (read: bug) is in system copper list in this particular situation.
I've not tried in a Setpatched system or KS <3.0.
Well, i'll check it
[EDIT:
mixed results
2.x and 3.1 is working properly, 1.3 and 3.0 copper HALT, <=1.2 same as 1.3/3.0 but different HALT code.
Actually if you use full compliant code (OpenScreen and company) or a full takeover you don't get this corner case.
But i'm constrained to a different solution. Anyway the patch is simple
]