I've been having a similar problem. But in my case the DC window doesn't close. It freezes for a while, then I get a warning box that a process is taking too long, do I want to cancel or wait, then it unfreezes with the search term still in the search window but the search not done. THEN I can hit return and the search will happen. I do not have this problem in M8.
But I've found a work-around: instead of typing the search term into the DC search box, type it in the notebook, highlight it, and hit F1. This works fine.