Are you able to include the full path with whatever wav program you would like to use, eg.
/usr/bin/play somesound.wav
I've just done a quick search, and it seems that other folk are having the same problem, - maybe the bug that was in the previous version was never fixed...
As a last resort, you could use another mail notification program (eg. that which comes with Gkrellm - definitely recommended) to check the mail server regularly, and only open the mail program when something interesting arrives