Thanks for the feedback! Let me explain why the icon changes and then see if you'd still want to disable it.
When the icon is in its normal state, pressing the "previous tab" shortcut (altA, by default) switches to the most recently used tab. As soon as it does so, the icon gets inverted. Pressing altA when the icon is inverted will actually switch to the tab used before the one you just switched to. If you keep pressing it while the icon is inverted, you'll go further back into the stack of tabs. After 750ms, the icon switches back to normal, and pressing altA will again switch to the most recently used tab.
As an example, let's say you open 5 tabs in order, so that tab E is the current one:
A B C D >E<
Pressing altA once will switch back to tab D: