puzzled by output of ReceiveMessages

[RootlessAgrarian]

Something is puzzling me about the output from this demo sketch. I have got some push buttons working on my Nextion, and am reading the serial port with a Uno successfully. I see this kind of output in my Monitor:

65 0 8 0 ffff ffff ffff
65 0 8 1 0 0 0 ffff ffff ffff
65 0 8 0 ffff ffff ffff
65 0 8 0 0 0 0 ffff ffff ffff

So far so good -- an on/off button id 8 on page 0 is pressed and released, and on the release event I send its id and also (in user code) package up a data message to send its state (selected); I press it again, and on release I get the release message again and my Nextion user code sends a further message with its state (deselected) and it's all fine. Except for those trailing EOM bytes!

The ITEAD doco says that the EOM marker is three bytes: 0xFF 0xFF 0xFF.

Yet the monitor is showing 6 bytes: FFFF FFFF FFFF.

I did take a look at the "listen" function and I don't see where those FFs are getting duplicated, yet when I print out my messages from the Nextion (user code) ending in FF FF FF, what I see in the log is FFFF FFFF FFFF. It's quite puzzling. I must be missing something obvious...!

[GeertvanWissen]

I think this had to do with the way "cmd" is stored in the Nextion::listen method. It is declared as an String object, but the individual characters are handled like the string is a null terminated char[] array. I'm not sure if this is possible like this, but it looks like we end up with a uint16_t number from the one byte that was received. I noticed that this 'bug' also messed up the coordinates when receiving data from "sendxy"