I'm thinking it's a proxy issue - part of the programming makes it so the devices (v2 blades and cube) restart when they don't get any work. All three restart simultaneously and the problem is most assuredly not heat related.
Sorry - just noticed you said it wasn't heat related. Okay; I too use Slush's proxy... I however, have a separate proxy for each cube because I became tired of troubleshooting issues related to using a single proxy. You could try my setup.
https://bitcointalk.org/index.php?topic=352658.msg4349054#msg4349054