UNIXCMD & unexplained stdout messages

I'm getting intermittent issues when using the UNIXCMD utility, it's
raising an error closing the UNIXCMD file (File spec that specifies
'UNIXCMD/UNIXCMDOA'). The actual command does work.

I can't replicate the issue when when re-running the identical command.
The command is a literal with placeholders that are replaced with actual
values.

RPG snippet:
lUnixCmd = 'zipnote "&ZIP" > "&TMP" +
&& echo ''&COMMENT'' >> "&TMP" +
&& zipnote -w "&ZIP" < "&TMP" +
&& rm "&TMP"';
lUnixCmd = %scanrpl('&COMMENT' :commentText :
%scanrpl('&TMP' :lTmpFile :
%scanrpl('&ZIP' :zipFile
:lUnixCmd)
));

Here are the stdout values that are returned by reading UNIXCMD:
rm: 001-2103 Error found getting information for file or directory
qsh: 001-0019 Error found searching for command FontBold.
qsh: 001-0019 Error found searching for command FontBold.

It's the FontBold messages that confuse me the most. I have no idea where
they come from. Is it possible that UNIXCMD is getting stdout from a
different command, possibly a Java process?

Any ideas?