How many of you deselect parts by clicking in an empty field? I think all.
Ok, this is what I noticed: if I click on an empty zone of a track inside loop locators, the part is deselected more slowly.
Clicking outside the locators the deselect is immediate. Same is if clicking on an automation lane inside locators.
Nothing important?.., but a bit strange.
Just wondering, what other ways are there that parts can be deselected?
Was just an introduction to the scene.
Could be that you can deselect also from Edit menu? 
Right so is there a default key command?
Also using any method other than white space, does that produce this sluggishness of which you speak?
Now I have noticed this (I have edited my post):
the slow deselect is only when clicking in a blank space of other track lanes.
If I click inside locators but on a blank space (not in a track lane) all go ok.
My deselections (clicking) are all done outside track areas.
Since I mainly use VST rack based instruments, what I do is I take the output busses out of the VST instruments folder in the tracklist and I then make copies of the blank folder(s) that remain(s); while deleting the original or copied names, so what I end up with basically amounts to project “dividers”.
This works well with many tracks since it means things aren’t all bunched up together and parts can run from beginning to end. Having said this, it would be nice if Steinberg could provide a formal means to divide the tracklist besides that arguably dorky method Divide Tracklist (kind of like ruler tracks in Nuendo, you can only have one in cubase wholly stupid ideas IMV).
I could upload a screenshot but hopefully I’ve explained it well enough.
I understand what you do, you have explained very well, but the slow deselection appear if you click on a blank space of your “dividers” too (in the range of loop locators only).
Have you noticed this?
Ah, that is where I must “dip out” of the discussion, as I do not have C6 (am waiting for 5.5.3 on Studio).
Cheers
This happen to me on C5 also.
Ok, since it is potentially likely that the C5.5.3 update will come before C6, maybe you could submit a new post in the C5 forum.