Yes, this has happened in previous versions but it seems
very intermittent. I've only had it happen once or twice. One theory is that because there are two different icon sizes, sometimes the wrong one gets picked. I don't know where this sits in the list of bug fix priorities.
Sixfinger
When this feature was first added I never thought I'd use it, but it really does help find tracks once they start adding up.
Same here. When they first showed up, I thought "Oh no, SONAR is turning into GarageBand" but it does help find tracks faster when you're scanning across channels in the console, especially when you also colorize related channels.
I wonder too where we might find more icons? I've made a few of my own, but could use icons of things I don't have such as a steel guitar....
One unnoticed feature in SONAR 2015 is that I contributed a bunch of soft synth and guitar icons. The soft synth ones were intended to be more readable replacements for the existing ones, the guitar icons were derived from Gibson's library of artwork so they were easy to find. There are a lot of public domain image sources on the net, but you can also use copyrighted images if they're for your own non-commercial use. You'll likely need a paint program that can resize, like GIMP (open source and free, very much like Photoshop).