I've noticed another audio bug in Presenter (including 7.05) but there is a workaround. I often export the audio as a single, long clip from pre-recorded lecture videos, and sync it with the powerpoint slides in Presenter. I've found it easiest to import the long audio file into the first slide, then sync using the Edit Audio window. I find that much easier to use than the Sync audio window.
However, If you use WAV format for the imported audio file, sometimes Presenter will simply refuse to play back anything beyond about 5 minutes into the timeline in the Edit Audio window. Nothing fixes it - restarting, re-importing, etc. However the problem goes away if you save the audio as mp3.