Network traffic altered when Logging enabled

I’m trying to resolve an outbound faxing issue.

Peforming a tcpdump on the asterisk box and sending a fax via an ATA shows that T38 appears to negotiate correctly. However, any T38 packets asterisk receives are not retransmitted to the ATA (similarly T38 packets from the ATA are not retransmitted to the receiving machine).

I perform a second test call after adding the line:

to the logger.conf file, and issuing a logger reload, and ensuring that core set debug is 1.
The tcpdump of this call shows a different problem. Between the time the reinvite to start a T38 session is sent to the receiving machine, and the time when the OK is transmitted back to my asterisk box, a few malformed RTP packets are received. Then my ATA sends out three T38 packets (which are not retransmitted). In the log there is a debug “Didn’t get frame from channel” message, and then the call is ended shortly later.

Disabling logging, and retesting yields the first result. Re-enabling logging and testing yields the second result.

So I am not sure what I can do at this point to assess the situation. It seems like the first result describes the problem at hand, while the second result is just an artifact of logging.
Any suggestions?