CLOG read problem after pg_basebackup

Hi all,

I'd like to ask for help clarifying an issue I'm having.

I've recently prepared new servers in another datacenter for some of our
databases which I want to set up as a streaming replicas. There are several
instances(clusters) with size ranging from 50-150GB. Some of them were set
up with no issue. Three of them failed to start after pg_basebackup
completed with:

FATAL: could not access status of transaction 923709700
DETAIL: Could not read from file "pg_clog/0370" at offset 237568: Success.

(the clog file differed in each case of course..)

As for PG versions one is 9.1.14 (on both master and replica) and the other
two 9.2.9 (also on both)

I've checked each file in question on the master server and in each case it
was last changed during the run of the pg_basebackup. I've copied the file
from master to the slave and it started normally, succesfully connected to
primary and everything seems ok since then.

My question is, why this is happening? Is it because the clog file was
copied by pg_basebackup before the trasaction status had been written to
it? Couldn't this information be recovered from xlog files?
Is my current solution safe for the database (I suppose so, but I'd rather
have it confirmed :) )

I'm puzzled as I haven't found this issue discussed at all so far and it
happened to me three times in one day on three different servers..

Thanks for any help.

Cheers.
Petr