Sorry I don't have an answer, riporto, but I am curious why for all of the many queries about the issue, no one seems to have an answer? Have I missed an update to correct this annoying issue?
Be sure you are up to date: The first line in Help > System Info should be: Adobe Photoshop Version: 2014.2.2 20141204.r.310 2014/12/04
Reset the Quick Selection tool by right-clicking on its' icon in the Option bar.
The second idea is to Reset your Preferences.
Press and hold Control - Shift - Alt immediately upon cold-starting Photoshop. If you get the keys down quickly enough - and you have to be VERY quick - it will prompt you to confirm deletion of your established preferences, which will lead to them all being set to defaults.
Not sure what did it in the end but latest updates and purging the cache seems to have fixed the problem. And reset the tool just for good measure
I solved this problem using your recommendation to reset my settings. The settings files must get corrupted from time to time. Remember to reset your Color Settings, Performance, and other settings. My Workspaces were not affected by the reset, so it was easy to choose my Workspace from the drop down.
The reset also solved a problem with previews in Photoshop appearing as if they had been extremely over- sharpened.
I'm glad you fixed your problem, but out of interest, what sort of lag times were you seeing? I ask because I seem to be having similar problems with Quick Select, and I am having to wait about a second or two every time I touch down with the QS brush. It never occurred to me to me to reset.
Trevor, do you recall that I recently posted about an inexplicable lag in layer operations? New adjustment layer, turning layers on and off, that sort of thing. Took several seconds on large files.
Then on a whim I reset preferences just because I sat around and was bored to death, not because it occurred to me for a split second that it would do any good. But it did. It fixed it, that's what it did.
The lag was very long. After dragging over a 4" square (on my monitor) area, it would take 25 seconds to be ready for the next drag.
After resetting, there is virtually no lag.
I have a i7-4930K @ 3.4gHz and 24 GB RAM, so I am used to very good performance.