ABS - REAR BRAKE PEDAL LOCK-UP

To me the advantages of ABS are worth the hassle.

I'm by no means an expert on antilock brakes, but to me it sounds like valve issue in the abs unit. Activating when it doesn't need to (at least on cars) is usually a wheel speed sensor going bad. Yours sounds like it isn't returning the brake to "man control" on occasion. Does the scan tool verify the wheel speed sensors are working ?
 
You've done my thought, change the fluid completely. My dealer is pushing me to do so due to mileage.
 
I'm a bit confused by the wording I think. Is the brake pedal just not moving on occasion or the rear tire is locking up and the ABS isn't activating?

If the brake pedal is not moving, check linkages and bushings
If the tire is locking up, enjoy the fishtails... just kidding. Possibly a caliper issue with the piston rubbing against something and not freeing up. Possibly a minor bend in the rotor or ABS rotor that is causing it to catch harder than it should.
 

Since you mentioned the DealerTool I have been thinking about buying it since it is not that pricey. I understand you have to send them some information from the first time use to get a key to make it function with your particular bike. If you retune your ECU, does that affect the Key they have sent you. Do you know??
 
I have the dealer tool and bike is not affected by a re -tune, probably apply to all dealertools
 
Check for codes first. some codes do not turn on check eng light.
on cars***if it has a dedicated fuse we sometimes pull it for checking purposes to see if it still has probs
after it does the prob u might carry a tool and loosen the bleeder to see if it has pressure.
make sure that pedal is returning to stop.