If my friend presses some memory buttons - the crash happens.
I fixed this problem with simple comments in the source code:
(in calculator.lua)
-- marcalc_mem = marcalc.add({type = "flow", name = "marcalc_mem", direction = "horizontal"})
-- marcalc_mem.add({type = "button", style="marcalc_button_style", caption = "ms", name="marcalc_button_MS"})
-- marcalc_mem.add({type = "button", style="marcalc_button_style", caption = "m+", name="marcalc_button_M+"})
-- marcalc_mem.add({type = "button", style="marcalc_button_style", caption = "m-", name="marcalc_button_M-"})
-- marcalc_mem.add({type = "button", style="marcalc_button_style", caption = "mr", name="marcalc_button_MR"})
(mb it's only our problem)