@Keith Was this part of the beta from v8.0 or included in later released v7.3.2 ? Because v7.3.2 doesn't seems to fix this issue...
So, I just installed the latest beta (version 2) on my work machine with a second taskbar. I used
7+ Taskbar Tweaker to get the process app id from the previously mentioned Atom editor and saved it. I can confirm that saving the process app id now does work. But I can't confirm that this setting does anything. What I expected to see was that there wouldn't appear an second icon beside the pinned Atom icon (see screenshot).
The documentation doesn't mention anything about how this setting exactly works.
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Just a heads up to let you know that in 8.0 Beta 5, there's a new Advanced Setting called "Group Buttons Only by App ID" that you can use to force it to only compare the App ID when grouping.
Hope that helps!