Since Special:Search got a new autocompletion thingy, the search bar got quite nasty. One specific behaviour, for instance, makes little sense.
1) Reach Special:Search
2) Click advanced search
3) If the cursor is not in the search bar, click it.
4) Click some checkbox
I. Observed: Search bar becomes red because it's empty. (Also happens in step 2 with monobook/Firefox 38 because the search bar is autofocused.)
5) Type something.
6) Delete the text to start typing from scratch.
II. Observed: Again the search bar becomes red.
I'm not sure if there is any case where Special:Search can correctly guess that I'm wrong in not typing something in the search bar. If the user didn't type anything, they probably have their reasons and will soon find out when they hit search anyway. Either the red alert is made much smarter, or it should be removed.
This is in 1.26wmf15 (fc35b2f).