Start date bug

Someone added tasks that had checked "Start date" option, and filled just start date, no due date. I don't know how, but it was added surely on mobile.

While I was editing it, I just copy-pasted start date to due date, unchecked "Start date" and added yearly recurring + unchecked copying subtasks.

After saving it still keeps start date making it same day. Like 1 Sep - 1 Sep.

It is reproduceable probably since same did occur for all 3 tasks.