I guess its a bug but if you have a workaround for this will be helpful.
I use checkboxes in grid how bug happen

I select 1 element or more then click Select all on top.
I have a button that I click in navButton and there I gather all checked elements using grid.getGridParam('selarrrow');
in array have 2 times preselected checkeboxes ids.
I can use distinct values or something but I think its a bug in grid function.