Create a task, set to waiting on a contact. Then remove “waiting” status. The contact for which the task was waiting is still associated with the task, but not included in the tags field.
Could not reliably reproduce.
Thanks for reporting!
I managed to reproduce the bug by dragging from “Waiting” to “Someday”.
Waiting → Inbox works correctly as a workaround to “clear” the contact, until the bug is fixed.