@Kovid - A week of running 3.8 and no icon separation - so maybe your changes made a difference.
But one other difference.
Before I installed 3.8, I unpinned the existing calibre icon*
I ran calibre from the install (I normally uncheck that box) and pinned that instance to the task bar.
I don't know why it should make a difference. I also don't know why echidnas lay eggs and hedgehogs don't.
- the icon I unpinned, would have been pinned from an execution instance created either by running Program Files\Calibre2\calibre.exe directly, or from running a start menu or desktop shortcut. As a rule, I don't run applications from installs, because after a download-and-install I normally move the install file elsewhere.
If AnotherCat and or Terisa de Morgan have nothing better to do, perhaps they could try unpinning their existing problematic icon, reinstall 3.8, run calibre from the install, and pin that icon instance.
BR