[Users] Process mark

[Adrian]

Up till a couple of days ago, hitting Del with a message header selected
in the list moved that message to Trash.  Recently that changed.

Now, when I delete a message from the inbox with the delete key,
- the message stays in the Inbox message list but is grayed out.
- a blue less-than mark appears.
- the Trash folder list entry goes purple.

When I change folders a dialogue box appears
   "Process mark
   Some marks are left. Process them?".
Answering Yes then moves the message to Trash.

I haven't changed any settings.  I'm running v 3.16.0.