Clipman panel plugin incorrectly remembering mouse selections

[Matt Connell]

Using XFCE version 4.18, with clipman plugin version 1.6.2

In short, clipman is capturing mouse selections despite my attempts to
disable it.  I have Behavior -> General -> "sync mouse selections"
disabled, and History -> "Ignore mouse selections" enabled, and I still
get anything that I highlight as a paste option in the list.

Is this a bug, or am I misunderstanding these configuration options?