Reading in "unspecified behavior" situation from serial port causes crash

I had just attached a serial port to a casing, and used a mechanical piston to push the casing towards an already-in-place C:C&A accumulator. The accumulator was already almost fully charged, way beyond the about 32k limit in serial protocole specification. I wrote a simple "mov left acc" program, inserted it in an execution module to the right of the serial port, attached a controller and used a supplementaries crank (akin to create analog lever, allows applying a specific redstone level) and applied power level 1, and after a moment - power level 2 which crashed immedietaly, presumably from attempting to read the value. Might actually be something wrong with the accumulator, idk.

Crash log: https://pastebin.com/sRk0EirT