ttyusb/uart sends 'USB' during transfer

I am using Go for a project and am transmitting data to an embedded device via the serial port (ttyusb). During fast and "large" transfers I've noticed that the transmitted data did not match the values I'd wanted to send.

I've tried various available libraries, in the end they all read and write using syscalls. So I've attached a Logic Analyzer to see what's going on.

Then I noticed that the data mismatch in the output had a clear pattern: Instead of sending my data the serial port would interleave my data with the following values:

0x55, 0x53, 0x42, 0x53, 0x70, 0x02

Followed by zeros (0x00). In total 22 Bytes. The total number of bytes transmitted via the serial line did match the number of bytes I wanted to write > so essentially my data was masked with these 22 Byte-Blocks. The weird thing is that I can translate those bytes to ASCII

0x55, 0x53, 0x42, 0x53, 0x70 = "USBSp"

Now my Question is: Can't I send arbitrary data (HEX values) over the serial port or are there some control characters that I should be aware of that would make the serial port send out Identity information or the like?