Regular failure to detect waiting cars.

The turn left lane from Quuns road upto London Street (from heading east to heading south) has repeatedly fails to recognise the cue of cara waiting to turn. I have been sat at the light for 3/4+ cycles of the full order of light changes at this turning more than once. I have seen lines of multiple cars sat waiting for several minutes for the light to change, the light sits on red until someone in one of the further back cars gets out walks over and tells the front car/two to move before it almost imidiatly cycles to the green. (Which is obviously not very safe). I think the induction loop is either broken, not sensitive enough, or in the wrong place. Perhaps a second further back to detect a cue could help.