From the 10.4R10 release notes:

http://www.juniper.net/techpubs/en_US/junos10.4/information-products/topic-collections/release-notes/10.4/index.html

A service technician brushed against the front panel of a MX RE card, and the RE powered down. Resulted in outages of customer networks. [PR/703076: This issue has been resolved.]

Sadly they have updated the document.