Normal Rex File Edit Behavior?

I don't ever remember having this issue before. 
 
I drag a Rex (.rx2) file from the Sonar media area and drop it on a new track at the first measure.  I'm not using the first 4 measures of the rex file, so I grab the handle and slide the start time over to measure 5.  I'm not moving the rex file, just cutting off the first 4 measures.  Now, I want to grab the whole track and slide it left to measure 1, but Sonar won't let me.  I can move the track right to a later measure, but not left to an earlier measure.  It's like Sonar still detects the track as starting on measure 1.  Is this normal behavior?
 
Now, if i right click the rex file and bounce to clip, afterwards I can move the bounced track left or right no problem. 

I think you nailed it. The graphic representation is just that - the underlying clip is the same, unless you trim it.

Groove Clips are a special case, and REX files are converted into Groove Clips upon being imported.