Error messages in a hot standby server's logfiles

Hi all,

My setup is: postgresql V9.3.3 running on a CentOS 6.5 (kernel 2.6.32-358.18.1.el6.x86_64) and I have 3 servers, one primary and two hot standbys. In our failover and loss of
communications testing, I have seen a couple of issues that I'm hard to explain. For instance, we took one hot standby out of service by shutting down postgresql on it. Now, we're
hot standby with log shipping as an insurance policy, so the WAL segments continued to be copied onto that out of service standby for a few minutes. On restart, I see:

cp: cannot stat '/mnt/wallogs/archive/0000000C.history': No such file or directory
cp: cannot stat '/mnt/wallogs/archive/0000000B0000001900000077': No such file or directory

Later in the logfile, I see another failure for 000000B.history.

In looking at the /mnt/wallogs/archive directory, those files aren't there, but as the primary never had an issue and continued to copy WAL segments to this directory, why was the
standby looking for them? What triggered this? Also, in that directory, I often see files generated by the pg_basebackup command used to build the standby, files like
"0000000B0000001900000000.00000028.backup" or generally files ending with .backup in their names. These never get removed automatically by the standby server. We have to manually
remove them. So, I'm guessing they weren't necessary, so why did the primary copy them here using its archive_command? Why aren't they removed by some mechanism on the standby?

--
Jay