..Well, whatever you do to address this, I'd look into installing some kind of independant indicator (LED light?) on your MH dash, and wire it to the brake switch on your toad somehow. That way, you'll know exactly when the toad brakes are being applied and released. I always recommend this, regardless what brake system you use.
..I will say also, that what happened to you here is the primary reason why I do not trust, and want nothing to do with any 'electronic box' type of brake system. Just too much potential for major damage to be done to the brakes. Real bad part is (as you found out), unless you install an independant brake indicator like I mentioned above, frequenly you won't know anything is wrong until major damage is already done. Your toad is typically sooo much smaller than the MH, the MH can drag the toad's brakes all day and you may or may not even notice.
I agree 100% with the earlier recommendation to get a Readybrake. Readybrake is only system I'll have. No electronics to foul up and damage your brakes. No way at all, really, for it (Readybrake) to ever over-brake your toad (as long as its initially installed and set up correctly). No electronics, nothing to put in and take out, and real simple one time cable installation on the toad. Just a simple, no-nonsense, cable operated surge braking system that simply works.