The Short Version
Performing a ‘filtered’ listing of tagged lists in the ‘Tags’ page is impossible when hide completed is also on.
The Long Version
I use tags for tasks and lists; but I use some tags only on lists, for example #project.
If I go to the ‘tasks’ page and I enter #project into the filter field, my lists are not displayed unless hide completed is also off.
This makes no sense, because the lists in question contain plenty of uncompleted tasks.