OK - I was able to re-create this, and now its gone away. (apparently for good).

Here's what I did.

When the problem occurred, I had filters turned off (the check box blank). Then I turned filters turned on (the check box ticked), but had no filter chosen (the unamed blank entry at the top of the list), and the program started correctly positioning to the edited Vendor.

I cannot get it to fail any longer, even with a machine reboot.