Slicer "Select All" Problem

I have a slicer where single select is OFF (since that is the only way I can show the "select all" option which I want). Multi-select with ctrl is ON. I noticed that when I leave "select all" alone, I am able to switch between my two slicer options with behavior that is comparable to "single select." That is, when one is selected and I select the other, the previous box becomes unshaded and the box that I clicked becomes shaded. However, when I click "select all" once, it selects all boxes as it is supposed to. But when I try to select one, single box again, the behavior is strange. It seems to be "stuck" on "multi-select" since the "select all" option must be switched "on." When I press "select all" again, the switch now seems to be "off" and I can single select again. Why is this? It is not that big of a deal but it could be confusing or frustrating for certain users viewing the published visualizations.