I'm surprised that the oven could melt solder joints. That oven must be really out of whack, or
they use low temperature solder.
I once used a toaster oven to bake some glass enamel onto a stained glass project I was doing. The enamel was supposed to cure at 325 degrees, so I set the oven to that, but it overcooked the enamel (the white turned brown) and melted absolutely all of the solder joints.
My theory is that while some part of the oven was at 325, and maybe even the average temperature was 325, there's a significant gradient close to the heating element.
I still use that toaster oven, but now I use an industrial PID controller and a thermocouple lying directly adjacent to the work to control the temperature.