I experience something similar to this on occasion when opening Chrome (using the setting to "restore last session"). It doesn't happen every time it seems, but once in a while on opening Chrome, some tabs (not pinned ones) will be hibernated when they were not previously hibernated, but will also get duplicated in non-hibernated form. 

Clicking on the hibernated one will open a new tab, while clicking on the duplicate will switch to the tab that was open from the last session already.

Chrome 21.0.1180.89 m

Windows 7 x64

Yes, I mean the tooltip when you hover over a row and it shows the item's title and URL