is it normal for a usb device o reset when windows enummerates the device
It depends on how the designer of the printer software designed the USB interface. Clearly, they either intentionally or accidentally created the USB software to reset when power is detected.

I would report the problem back to whomever wrote the code. I agree that is an undesirable behavior and it could very likely be fixed easily in the code.

However, it is never safe to assume how ANY hardware will behave when "hot-plugged" (which is essentially what you did).  I would NEVER leave something like that plugged in when powering up the computer. As you have demonstrated, you never know exactly what will happen.