The following is not a bug in SimulIDE, because the function of the register OSCCAL (in ATmega8, for example) is not important. The MCU frequency is set manually at will.
So, I noticed now that OSCCAL register is inactive and set to a fixed value [0x00]
I guess, for debugging certain codes, making OSCCAL as an I/O register (which could be written and read) without having any function will help. Thank you.