The basic problem is that when you transfer a registration away from Dreamhost, DH does not (in the cases that I've experienced) know that the registration is gone. Also, there is no way in the panel for a customer to tell DH that the registration is gone.
As a result, some considerable time later ... and even though you have since renewed the domain with another registrar ... when the original expiration time of the domain as of when Dreamhost last knew about it comes up, DH sends you an email which says:
Thank you for being such a flakey registration company. A useful reminder of the impermanence of everything.
(footnote: it is a false alarm; yourdomain.com has not actually been deleted from the registry ... hopefully)