Multiple Tabs in IDE

In the settings, I have it set to “open item in new tab” when I double click. When I do that, a new tab opens and had a lock icon. What’s that icon for?

Also, lets say I have a class with three methods (M1, M2 and M3). The Navigator is showing the full contents and I will have M1 will be open (no other tabs). When I double click on M2, M2 actually opens in tab 1, and then opens in the new tab. So both tab 1 and tab 1 have the same code. So I lose my spot in tab 1. It looks like double clicking on an item give it focus for the current window, then opens it in a new tab. Is there some kind of work around for this?