We, too, had (have) this issue. The only work around was to respond within "Tickets" and use your CRM signature.
This works alright once we got the hang of it, but working directly within Conversations is much more streamlined and thus a time saver for our org as well.
Agreed - this seems like a very basic feature to have in any sort of emailing tool. It's surprising that it isn't included. It's stopping us from fully moving over to Conversations which is very disappointing as it was one of the main reasons we purchased the service platform.
