Hi,
I was trying to work out that Custom Search in Filters does indeed work the same way that the search tab does and I was getting crazy returns. Then I tumbled to the fact that Custom Search was case sensitive!
Nobody is going to expect that. They'll just be beefed when their searches don't come back with the expected results.
I guess the right answer here is to include a case sensitivity toggle for this search box as well as the one in the search pane, given that, if I have this right, the point of giving Filters a separate search box was that and-ing functions from one pane to another would be bad. (Agreed, BTW). So, just applying the state of the button from the main search pane wouldn't be a good option.
[insert here my standard rant about case sensitivity being the biggest self-inflicted wound in the history of special libraries]
-Carl
PS: I don't know if users are going to appreciate how radically cool the way you've done string vs whole-word searches is. But it rocks! (I was mixing the two in one query when I ran into the case sensitivity issue.)