When a grid header cell is sizable and sortable at the same time, the mouse cursor style does not reflect that the column is sizable when hovering the resize handle of the column header (draggable region at the right).

This happens because a sortable column header has a more specific css rule overiding the cursor style of a resizable column.

style applied when hovering the resize-handle:

.z-column-sizing, .z-column-sizing .z-column-button, .z-column-sizing.z-column-sort .z-column-button {
  cursor: e-resize;
}

overriding style when hovering a sortable column:

.z-column-sort .z-column-content {
  cursor: pointer; /*more specific than the rule above*/
}

also check the attached example (including the workaround, but commented out)

Workaround is to put this more specific css-rule on your page, which overrides the pointer style again:

<style>
	.z-column-sort.z-column-sizing .z-column-content {
		cursor: e-resize;
	}
</style>