Double-clicking on a window’s Title bar (1) in order to reduce it to the bar is probably used by lots of people, and so is, I believe, double-clicking on a word or a piece of text (2) in order to select it — a very standard procedure. A conflict arises when you have a string in the Search field that you want to replace by selecting it and entering another one: you end up with (1), i.e. reducing the window. When the window is restored, the contents of the Search field are the same as before, neither erased nor selected.
It is possible to remove the string in the Search box without selecting it, either by using the Escape key or by pressing Backspace repeatedly. But these methods are not standard, IMO. One solution would be to have a real Title bar on all windows, as is the case in most applications (at least on Macs.)
I’d like to hear about possible solutions before requesting a new feature or reporting a bug.