Sounds like a bug. The intended behaviour is:
- "One Click Highlight" on, Highlight assigned to RMB or MMB: Click the lemming with RMB or MMB to highlight it
- "One Click Highlight" off, Highlight assigned to RMB or MMB: Hold the RMB / MMB and left-click a lemming to highlight it
- Any setting for "One Click Highlight", Highlight assigned to a keyboard key: Hold the key and left-click a lemming to highlight it
Default settings should be One-Click Highlight on, and Highlight assigned to RMB.
I'll check that all combinations and defaults are still performing as intended, and fix them up if they're not.
EDIT: Just checked, and at least for me, everything is working as intended. If the above behaviours aren't working for you (as opposed to just misunderstanding how they should work, which would simply suggest better explanations is needed somewhere), can you come on #neolemmix?