For anyone who might be interested, here's an update: I purchased a
Syba PCI-E 2 port serial card and installed it. The polling behavior
is not evident on either port of the card. It remains evident when I
use any USB-to-serial adapter, just as before.
A very strange problem that I do not understand. The on-board COM
port is usually (but not always) a true serial port with a 16C550
UART as part of the Southbridge chip. However, on this board, that
may not be the case.
Regardless, I have a work-around!
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