If you're a user of the Stata statistical app, you may find it hangs when merging databases if Witch is running. The only apparent solution is to disable Witch before launching Stata. There is, however, an easier solution: Use Witch's blacklist.

Open Witch's preferences, and select the Advanced tab. Near the bottom is an input box labeled "Disable hot keys for apps:" Click in that box, and enter this text:

StataSE.app

Witch will no longer listen for its hot keys when Stata is the foreground app. Based on user reports, this will prevent the hang seen in Stata when merging databases with Witch active. (Unfortunately, we can't do anything about the hang in Stata; we'd need to work with Stata's developers to figure out why it's hanging.)