The new /etc/conf.modules is created in /tmp and then rename()d to /etc/conf.modules. This call fails of course when /tmp is on a different file system than /etc. Once I manually copied the file sndconfig worked without any manual intervention. I am impressed.
Let me run this setup by you, as I had no trouble in the test lab. I installed the /tmp partition on an IDE drive and put the / partition on a SCSI drive and then performed the installation. There was no problem with the conf.modules file and I was able to run sndconfig without any problems.
It did? I'm surprised. Yes, it's a bug, it's fixed in sndconfig >= 0.27.2.