Oxygen refuses to merge points

[Col. Faulkner]

I'm finding on some occasions that the "merge points"  
command (Shift-D) isn't working. I select two points I
want to merge, do Shift-D (or use the menu command)
but the points remain unmerged. Has anyone else
encountered this? Are there any circumstances where
this is known not to work?

My Oxygen is the latest release version (I cannot find any
way to retrieve or display the exact version number).

[Scars09]

works for me, should be the actual version that i use.
did you check the functionality of your shift key? sure you did, sorry for the stupid question, but i cant imagine anything else that could prevent the merge.

[DMarkwick]

Is there a minimum distance parameter in preferences?