According to the U.S. Consumer Product Safety Commission (a government agency), the problem is that "electrical arcing can occur in the machine's power supply, posing a risk of fire."
The Designer I machines typically sell for over US$5,000, so this issue is likely to be of greatest interest to very serious amateur or professional costumers. The linked page (see below) has a list of serial numbers and manufacture dates, and a description of the machine, so that you can tell for sure if your unit is affected.
Thanks to William from the Midrealm who provided this link.

My wife works for the company