Reminder with custom date defaults to 1969?

I am self-hosting the latest version of Vikunja (0.23.0) and reminders email normally. However, I have an issue with setting a “Custom” reminder. Vikunja ignores the relative time and always assigns the alert to December 31, 1969. (Note that only selecting “Custom” shows this behavior. The other options work as expected.) Here are screenshots to illustrate the behavior:

In this image, I have created a task due on May 29 and am setting a reminder for a week before.

After I click confirm, the reminder shows a date of Dec 31, 1969. Why? Is there a wrong setting somewhere?


Update: This is a known bug.

There is a GitHub discussion and it is fixed in the current unstable branch.