I think that the system looks harder at startup - probably before any interfering extensions can insert a new, troublesome driver into the loading sequence that might select fewer format options.
I had some trouble like this once [obviously]. I discovered the technique because I left the unreadable disc in the holder. The next restart caused it to appear, hence the advice.
Another tip: If your G5 has a little red light on and the fans run only at full speed, your RAM is installed wrong. Guess how I discovered that.
Given enough rope, I would discover America by getting lost, but I think that it has been done.
Dwight Atkinson