Possibly related - since the advent of Eclipse Designer , I have seen sporadic interference with other apps, and I'm thinking it could be JVM issues or memory resource issues. The apps that I have had the most consistent trouble with when running DDE are:
Mirth Connect Administrator - gets flaky and freezes (it's another eclipse based app)
Radmin viewer client - won't connect to to remote computers
All I have to do is close one of the competing apps (or reboot if it's too late) and these problems resolve.