TStringGrid.TitleStyle := tsNative - Fixed cells are not properly aligned

[apeoperaio]

Dear all,
I noticed a strange behaviour on Cocoa when using a TStringGrid.
If I set TitleStyle:= tsNative the fixed cells belonging to the fixed cols are not properly aligned with the floating cells.
See attached image.
Bug or feature?

Lazarus 2.2.0RC3 (rev lazarus_2_2_0_RC2-63-g3f5c16d5f9) FPC 3.2.0 x86_64-darwin-cocoa

[apeoperaio]

Anyone else noticed it?

[wp]

Checked on my VM (Mojave 10.14), and can confirm the issue, but only partly because there is also a top line, and this looks exactly the way how a HeaderControl (the upper control in the attached screenshot) is painted. I don't have much experience with mac, but could it be that this is the way the cocoa "themeservices" draw a header?