When I am working in InDesign using the tab ruler, then go to another program, whether its an option-click to hide InDesign or clicking on another program's window, either way the tab ruler stays up while all of InDesign's and its pallets and art boards disappear. It's kind of annoying that it actually has to be clicked to close so it goes away.
That is not normal. What version of ID? What O/S?
I'm running Mountain Lion on an Intel Mac, version 8 of ID in CS6. But I've seen this problem since CS4 on on a PPC. It's like the tab ruler isn't connected or related to InDesign. While all of the other pallet windows become inactive and disappear, the tab ruler stays right there on the screen.