As per the reference:
The order of the rollups will be saved in the file RollupOrder.cfg (in ASCII), which is located in the UI directory. Deleting this file, or removing an entry for a specific Class, will reset the Rollout order.
Or you could close max so that it won't accidentaly override it, and edit the file by hand. For example, the Editable Poly section looks like this in mine (the order number is what sets the order of rollouts):
Editable Poly SuperClassID <0x00000010> ClassID <0x1bf8338d,0x192f6098> :
Title <Selection> Order <1>
Title <Soft Selection> Order <3>
Title <Edit Geometry> Order <2>
Title <Subdivision Surface> Order <3>
Title <Subdivision Displacement> Order <4>
Title <Paint Deformation> Order <5>
Title <Edit Polygons> Order <2>
Title <Polygon: Material IDs> Order <4000>
Title <Polygon: Smoothing Groups> Order <4000>
Title <Polygon: Vertex Colors> Order <4000>
Title <Edit Elements> Order <2>
Title <Edit Borders> Order <2>
Title <Edit Vertices> Order <2>
Title <Vertex Properties> Order <4000>
Title <Edit Edges> Order <2>
I guess that 4000 is just some arbitrary number to make sure those rollouts show at the very end.
The file should also change whenever you reorder the rollouts by dragging them (mine does, immediately), so if that works and it somehow resets, it might be a good idea to make the file read only as soon as you are happy with the current order.