So I tried this out with the usage case you were using:
1st try preheating...
Does not stop the pre heat process.
Must disconnect and reconnect to proceed.
When trying to print from the reconnect steppers move slow and sound distressed.
Hit Emergency Stop and reconnected and then print appears to be okay.
And I did indeed see what you were describing.
- Sent a print job to the printer
- hit "Stop" in the MCP during the pre-heating stage, the printer was still in the pre-heat stage
- disconnected/reconnected, from here it connected but in the communication window, you can see S3D tell you there were packet transmission failures when it reconnected. My guess is this is due to it still being in the pre-heat process. With that error appearing in the comm window, I was expecting it to not print properly. Comm errors are a good sign for you to not proceed, and instead try to e-stop it or power cycle and reconnect so that you don't have any packet transmission errors
- went ahead and tried to resend the print anyways, it homed properly but then went into a random location.
If you stop the printer mid print (after the pre-heating stage) I've found that it operates as it should and I could resend a print job if I liked. It's possible the firmware implements a set temperature and wait like Marlin does, and recognizes the command s3d sends it for the "stop" command, but in the firmware level that will act funky with teh machine state being in both a stop state and pre-heating state.