To clarify, the odd behaviour I'm referring to starts to rear its head when (IIRC) you groove-loop the split clip, or it's used in a step sequencer context.  I'll need to experiment a bit to come up with a step by step sequence which illustrates this.  Please note that I was using the word hanging in a figurative sense (see my previous explanation), i.e. I did not at all mean to imply that it sounds continuously or anything like that.
 
My contention is that Sonar should ask the user how the situation should be handled and then take the appropriate action.

subtlearts

bapu
I've seen what ston is talking about.
 
Rears it's head if you split across a note the delete the right hand clip (i.e. no more MIDI to the right)
 
The cutoff note will simply continue to play for the duration of the song.
 
I've just learned to trim the note before I split.

Hmmm. Have you tried it in Platinum? 

No, but I will.

ston
To clarify, the odd behaviour I'm referring to starts to rear its head when (IIRC) you groove-loop the split clip, or it's used in a step sequencer context.  I'll need to experiment a bit to come up with a step by step sequence which illustrates this.  Please note that I was using the word hanging in a figurative sense (see my previous explanation), i.e. I did not at all mean to imply that it sounds continuously or anything like that.
 
My contention is that Sonar should ask the user how the situation should be handled and then take the appropriate action.

OK, I don't use the step sequencer much (at all, really) and I haven't experimented with groove clip looping yet in Platinum, so I'll have a look at those if I have a moment later in the day. Maybe we can isolate a repeatable bug or instability.

OK I played around with groove clip looping and step sequencer clips to see if I could identify any strange or unstable behaviour. Again, this is in Platinum, I might get around to firing up X3 again to see if it's any different.
 
So far, nothing. In fact, a step sequencer clip apparently can't be split at all, pressing S has no effect. Which is kind of odd, but there it is. A Groove clip behaves exactly the way a normal clip does - if I split it in the middle of a note, it non-destructively truncates that note, but if I subsequently manipulate the clip length it restores it to its original length or any part thereof, but so far it does so cleanly, with no hanging notes, meaning the clip end is producing a note-off wherever it truncates the note, and this seems stable and flexible.
 
Again, it seems to me that this is an acceptable state of affairs, at least as a default behaviour. So I would propose that your idea to have selectable behaviour is more of a feature request than a bug. It basically doesn't strike me as a big problem, but you might find others to support your position...