I have the same issue as Marc.
Your suggestion is a workaround, but not a solution.
Previously, any technician would have a custom signature that would apply to any Request to which they reply. Now, the only option is to have the reply template apply very limited metadata from the ticket itself. (i.e. If I reply to a ticket that someone else is assigned, their metadata/name will be populated in the template; not mine).
I think Marc was right -- it's likely that in an effort to fix the duplication issue, something was disabled/broken re: personalized signatures.
Can we be sure this gets fixed asap / in the next release?