I will make it short since this thread is already a tragedy (sorry MAHMUT).

• You stated that "DEC ECX" can crash something. This is why I asked you to explain that.
• "MOV EAX, EAX" is an effective "NOP". It does nothing expect modifying EIP. No procedure starts at 00403ECE, it starts at 00403ED0.
• You started with your "middle" instructions. When you put two "DEC ECX" right after each other but put a breakpoint on execution on the second one, "middle" instructions will get executed.
• We have no interpreter here. When I use an interpreter which formats your hard disc when it encounters 0x49 ("DEC ECX") than of course this "bytecode" can do anything. But it is no longer a "DEC ECX" in this context.