Checking the schematics:
https://github.com/dreamcat4/t12-t245-controllers-docs/blob/master/controllers/stm32-t12-oled/v1.5-ptdreamer-orig/iron.pdfHoly crap, who designed the v1.5? That's not how it's supposed to be!
2K2 resistors (R9, R10) provide little isolation against 24V short. The 24V would see them in parallel, connected to 3,3V (stm32 clamping diode)
So 1.1K to the 3.3V line, injecting ~20mA, which is a lot of current for the stm32 and the oled, probably rising the voltage in the 3.3V rail to dangerous levels.
Replace them with 10K, or even 47K!
Also, the diode should be after the resistor, at the side of the stm32 pin, so the resistor limits the current in case of a short, and nothing gets damaged.
Ricktendo also has a v1.5, maybe he can try...
I also thought about that time ago, seems reasonable.
Setting the initial temp, setting the temperature each time you turn on the station it's not a huge pain.
In any case, for 100K flash erase/write lifespan, if you change it 50 times a day it would take 5.5 years.
But yes, not an important option to justify the additional flash wear, also being the most changing option.
Edit: Done. Setpoint is no longer saved. Add new option in iron settings, "User temperature", which is applied at boot.