Step sequencer - annoying problem with unlinking linked clips

Got a niggling problem with unlinking clips, which I hoping you guys/gals will be able to assist with.
 
I use Addictive Drums 2 and the step sequencer to “program” the drum tracks, from the ground up (without using the pre-defined clips provided). I don’t use the step sequencer for anything else, so not sure whether this is AD2 specific, or not.
 
My normal process is to create a series of multiple 2/4/8-bar clips for intro, verse, chorus, etc., then “select” the set of clips (<shift>+<right-click> on the first and last) that I want to duplicate, select <copy>, then <paste> at the point that I want them to be - they appear as linked clips which is what I want. I then effectively repeat the same process n-number of times to “create” the main parts of the full drum track, with some non-linked clips sprinkled across the track for intros, 1-off breaks etc.
 
Occasionally, to emphasise a particular spot in the song, I’ll want to change a single 4-bar clip, for example, add an extra beat, or a roll, into a specific verse, without that same change appearing all the other copied & linked “verses” – so, therefore, I’ll <right-click> on the clip I want to modify, the pop-up menu appears and I select <unlink>.
 
And this is where the problem occurs:
 
Sometimes it’ll work just fine, and the single clip I’ve selected is the only clip that’s “unlinked”, and sometimes (and very frustratingly) ALL clips across the whole drum track are unlinked, regardless of whether they’re “linked” to the one I’m trying to unlink, or not.
 
To start with I’d suspected this was a project “setup/config” issue, but it appears this “unlink everything” feature occurs seemingly randomly across any project, regardless of whether it’s happened in that project before, and typically occurs when I least expect it to (i.e. typically when I’ve stupidly not pressed “save” before adding that 1 extra snare beat into that one particular clip).
 
I strongly suspect this is a “user” problem, not a software problem, so there might be some basic step sequencer principles I’m missing – for instance should I be grouping clips instead of linking clips, would that make any difference, I don’t know. I’ve browsed manuals, online help, and this forum, but haven’t come across anything similar, or any indications of why this problems occurring – this isn’t stopping me, it’s just annoying me.
 
Thanks in advance .... Kimbo