If I select multiple tracks the track numbers go blue.
 
I can now put the mouse at the end of one track, drag and change the length, and all selected tracks change together.
 
But if I try press Ctrl first (right edge of clip changes from dark blue to yellow) to compress/expand the clip, only the track I am on changes, not all selected tracks.
 
Have I missed something? Is this a bug?

This might help:
http://forum.cakewalk.com/CWBRN34569-Usability-problem-with-Stretch-MIDI-Clips-m3268750.aspx
 

Yes, I think I see the problem.
 
To me, with what I am doing now, it seems obvious that 8 tracks from 8 microphones on a drum kit, recorded at the same time with exactly the same starting time and length, should be stretched and shrunk by exactly the same amount.
 
But what if the clips are different lengths, or multiple clips in one track? I can think of at least 3 different behaviors one could want, there may be more. And with different lengths, what about peak positioning algorithms? You'd have horrible phasing effects.
 
I get it.
 
Anyway, it's easy to shift and align them manually. I did it in a minute.
 
Thanks for the deeper insight.