Unable to Create/Modify Pre‑1970 Recurring Events

Hello community,

I am running an Axigen Mail Server 10.6.29 on a Linux Debian 11 system. Since one of the last updates (10.6.28 or 10.6.27), I can no longer create recurring events dated before 1970. As soon as the year is 1969 or earlier, the event can no longer be saved. Existing events also cannot be modified — that also results in an error. Creating such an event through an external client (e.g., Thunderbird or calendar synchronization from a mobile phone) does not work either.

Is this a known issue, and is there a solution for it?

Thanks a lot for your help in advance!

Greetings MadCat

Edit: Debian Version corrected