Turn signal / hazards problem

I'm experiencing an electrical problem with a 1999 Cherokee Sport; all electrics on the vehicle are factory spec with no modifications.

Turn signals, hazard lights, brake lights, headlights etc all work (i.e. light up/flash) okay.
But, if I put on the left turn signal then *both* rear flashers go into blinking mode. Just the rear flashers - only one front flasher blinks (on the correct side).

The problem doesn't occur when applying the right turn signal.

Does this mean a duff flasher unit (and hence pretty cheap/easy to replace), or something more complex?

Any advice appreciated, thanks.

wow i would say.. make sure your trailer lights didn't get pinched or pulled then if that don't work i would call the dealer sorry if that don't help