omap-u-boot-utils: ukermit error with serial file transfer

I originally emailed Nishanth, who suggested moving the discussion to this
I have encountered a problem whilst transferring files to my Beagleboard rev
C2, which has U-Boot 2009.01-dirty.

When I run ukermit (on /dev/ttyS0), the file transfer begins, but eventually
fails with the following error (and the board stuck):

Downloading file: 26.457% completed(1733900/6553600 bytes)Failed after 4
retries in sequence 59 - success send = 1733900 bytes
Data transmit failed

The problem occurs each time at close to, but not exactly at the 1.7MB mark --
Another run (this time trying with a delay added: '-d 500', and a different
loadb address: 81000000) gave the following:
Failed after 4 retries in sequence 65 - success send = 1734500 bytes

I have managed to find a bizarre work-around: The transfer always happens
correctly if I am connected at the same time using minicom with the usbtty
device (/dev/ttyACM0, with ukermit using /dev/ttyS0).

I would be grateful to know if anyone has experienced the same issue, or has
any ideas about the cause.