Turn SMTP Proxy on, all mail flow stops

Running 9.400-9 On Saturday I noticed that I hadn't received any emails for a long time. After much investigation, turned off the SMTP proxy. Everyone started receiving emails, and they should be sent to external addresses as well.

Looks like I'm not the only one having this issue:


Nothing in the logs. Rebooting the system doesn't help.

Thought I'd post it here, as 9.4 is still considered beta?

Anyway, it's obviously a pretty important issue!

Known bug or something specific to my (and others') configurations?