The node's parent is a tilemap and this tilemap is to 0, 0, no differances using position or global position in this case.
But, i found something interresting: if i disable the "expand" option of the textureButton's node, my buttons are well positioned in the gridContainer. Adjusting the GrindContainer's anchor prevent overlap betweed buttons and panel font.
The textureButton node locked the texture to the top-left but in my case, it's not a problem.
I think the problem is solved.
Thank you for your attention, Megalomaniak.