Well, I got the serial function working reliably by doing this:

hserIN 65535, oops, [STR smallp\12\10]

rather than this:

hserIN 65535, oops, [STR smallp\12\13]

aparently the linefeed was the last command sent, so by terminating with a carraige return, the linefeed that followed was polluting the serial stream for the next packet