Series Selection

ASJones[CodePlex]
In using the Simple Filter for series selection, I can select a Site, but often the Variable selection is grayed out and I am unable to select a Variable. This sometimes occurs after a site has been selected, but it always occurs when no site is selected
and only the Variable filter box is selected, so I effectively can't select by variable alone.

Start by reproducing the issue in the Simple Filter's series-selection UI: test Variable selection with a Site selected, after selecting a Site, and with no Site selected. The payload names no source file or test; done means Variable selection remains enabled and variable-only filtering works in each case.

Written by the indexing model from the issue text.