[plt-scheme] sporadic seconds->date error when doing setup-plt -l

This sporadic error has happened to me twice.  Once just now, and once 
approx. 24 hours ago.

The error did not exhibit on an immediate subsequent run of "setup-plt 
-l sicp", nor when re-run after cleaning all compilation artifacts in 
the collection directory.

setup-plt -l sicp
setup-plt: version: 4.1.5 [3m]
setup-plt: variants:  3m cgc
setup-plt: main collects: /usr/local/plt-4.1.5/lib/plt/collects
setup-plt: collects paths:
setup-plt:   /home/neil/scheme
setup-plt:   /home/neil/.plt-scheme/4.1.5/collects
setup-plt:   /usr/local/plt-4.1.5/lib/plt/collects
setup-plt: --- pre-installing collections ---
setup-plt: --- compiling collections ---
setup-plt: making: /home/neil/scheme/sicp (SICP)
setup-plt:  in /home/neil/scheme/sicp/
seconds->date: expects argument of type <exact integer>; given 
#(struct:date 19 30 1 4 5 2009 1 123 #t -14400)
setup-plt: making: /home/neil/scheme/sicp/lang
setup-plt: --- updating info-domain tables ---
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