semi-preditcable OTPs

[Travis H.]

I recall reading somewhere that the NSA got ahold of some KGB numeric
OTPs (in the standard five-digit groups).  They found that they
contained corrections, typos, and showed definite non-random
characteristics.  Specifically, they had a definite left-hand
right-hand alternation, and tended to not have enough repeated digits,
as though typists had been told to type random numbers.  Despite this,
the NSA wasn't able to crack any messages.

My question is, why?   I think I know the reason, and that is that any
predictability in a symbol of the OTP correlated to a predictability
in only one plaintext symbol.  In other words, there was no "leverage"
whereby that plaintext could then be used to derive other symbols. 
Can anyone explain this better (or more accurately)?  Is this lack of
diffusion?  Or does it have something to do with the unicity distance?
--
http://www.lightconsulting.com/~travis/  -><-
"We already have enough fast, insecure systems." -- Schneier & Ferguson
GPG fingerprint: 50A1 15C5 A9DE 23B9 ED98 C93E 38E9 204A 94C2 641B

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