Garmin 305 Question, Biking showing up as MultiSport

I had this issue as well for my first workout.  I'm fairly sure I resolved the issue by turning the auto multisport option off.

What I do is hold the "reset" button when starting a workout that is not part of a multisport event. It only takes 3 seconds before you start.
I love the multisport feature.

Have you tried using Sports Tracks?  It's far better than garmin's software for data analyzing.

Correct.  Basically there are 2 options with the multisport mode, Auto and manual.  Auto you go in and set up and when you hit the lap button it goes to the next sport.  Manual works a little different.  Lets say you go for a run on Monday and want to ride on Tuesday so you turn your watch on and hold in the mode button and switch to bike mode.  If this is all you do you will be in multisport mode because you have not held the reset button in.  You can also place your 305 on the cradle to charge and that also resets it I believe.