When I'm in Enhanced Clips Mode, particularly Edit Clips Mode, and I expand a clip that's been cropped, for some unknown reason, Sonar seems to want to add empty bars to my project. For example, My project is supposed to end at Bar 111, beat 4, tick 920, and I've trimmed a clip so that it starts at Bar 89 rather than at the beginning (Bar 1). When I expand the clip to start at the beginning, that's where it seems to want to add those empty bars. How do I make it so Sonar doesn't do this strange behavior?

Can you clarify where bars are being added? Do you mean clips that were staring earlier earlier start later after editing the one clip's edge earlier?
 
Or are you just talking about the clip you're editing? If you slip-edit past the point where there are any data in the clip, SONAR will add empty space to the front of the clip. Is that the problem? If you want SONAR to repeat the existing clip content starting earlier in the project, you'll need to convert it to a Groove Clip before slip-editing by pressing Ctrl+L. But I just tried it, and "cropping" in Enhanced Editing mode is not the same as slip-editing a groove clip with the mouse; it still just adds empty space, rather than 'rolling out' copies of the data.
 
Enhanced Editing is a very old feature that never got much love from users, so it never kept up with the addition of new features like Groove Clip Looping and Slip-Editing, and was already becoming obsolete in 8.5.
 
But maybe that's not what you're after, either.

What seems to be happening is, when I expand a clip to show more of the original audio, Sonar puts empty space at the end of the project. What's up with that?

Meaning you have Stop At Project End enabled in Track View Options, and playback doesn't stop at the same place after cropping the start point of a clip? I'm not seeing that. Do you by any chance have Move Over to Make Room enabled in Preferences > Editing > Drag and Drop?

brundlefly
Meaning you have Stop At Project End enabled in Track View Options, and playback doesn't stop at the same place after cropping the start point of a clip? I'm not seeing that. Do you by any chance have Move Over to Make Room enabled in Preferences > Editing > Drag and Drop?

No, I actually have "Blend Old And New" checked in Drag And Drop. Also, I have "Stop At Project End" checked, and it stops at the end if the clips are left unchaged or have been trimmed. It's when I expand them to show the original audio that was trimmed from the left side.