Not true. This is a problem during PvP when someone tries to interlock the opposing player at the same time as you, opposed to just interlocking someone who is obviously engaged with another player. 4 seconds is plenty of time to get sniped, knifed, etc, so it is kind of annoying.
Even if it's not a bug, I do find this annoying too. I'd love to see my engage-interlock button grayed out if my target is in interlock.