Duplicated tabs would 'vanish' until browser restart

[dsl101]

I recently ran into an issue where clicking 'Duplicate tab' in the TST context menu would duplicate the tab, but it would appear and then quickly vanish in the TST panel. Closing and restarting the browser would show both the original and duplicate in TST, but every time after duplicating, it needs a restart.

On a clean profile I was able to find the culprit: delayForDuplicatedTabDetection in the Development settings (Delay to detect duplicated tabs). This has been configured as 320 since I can remember, and just now it seemed to stop working. The only value that I've found now where duplicated tabs show up properly is 0, so I've changed it to that.

But what is that setting about? What is it trying to cater for? I couldn't find any direct documentation on this setting, and since it's now working (at least for duplicating individual tabs), I'm ok with that. But what else might reducing this value break?