Arduino Mega Reset not working when Serial Data is sent


I'm building a 2 DOF Simulator with an Arduino Mega as Controller.

I've cabled an Button to the Arduino to Reset it in case i want to reset the Program.

The RESET Input of Arduino is pulled to 5V with an external 4.7k Resistor when Button not pressed. When pressed then GND is switched to RESET Pin.

The Button works fine as long as there is no Serial Data transmitted. As soon as Data is transmitted during Reset Button is pressed Arduino seems to hang.

Basically the following is happening: 1.) Press Reset Button -> Arduino Resets normally 2.) Enable Serial Transmission from PC (SimTools) to Arduino -> RX LED on Arduino Lights up (Sending Values every 2millis) 3.) Arduino is carrying out the Movements as expected 4.) Press the Reset Button during Serial Data is reveiced from PC -> Arduino seems to Reset (All Outputs are switching off), but does not recover from Reset. No Codeline seems to be carried out. For testing i'm switching off Status LED in first Line of Setup Function. But Status LED not switching off 5.) Disable Serial sending from PC 6.) Around 2 Seconds later, Arduino seems to recover. Status LED switches off, Code starts to run again

Very strange behavior. Does maybe somebody has a hint for me what's going on?

Thanks a lot, Markus

Is it possible that the Arduino is going to some sort of "Software Download" Mode?

I mean pressing the Reset Button during Serial is active might cause the Arduino to somehow stop and wait for Software download.

When Serial Transmission stops it reboots automatically...