I wonder if anybody ever had such an issue...The flip flop button on my transponder is super sensitive. The unit will flip flop to the standby code just from random vibrations. Eventually, I think the quick flip flopping locks up the unit, and I am unable to enter a new standby code. I have to shut it off for quite a while to get it to work again. Although the unit is 20 years old, it has seen little use, and has been well cared for. I do have a tech lined up to look at it, but I don't want to spend a lot on this old thang. My temporary get around is to put 1200 in active and standby, which is fine until I am asked to squawk a certain code.