Thanks for posting about this. I recommend un-retiring that bike temporarily so you can check and edit any defaults that may still be set. To do this:
Go to your Gear page on the web here: https://www.strava.com/settings/gear
Look for your "retired bikes" link and click that to show the list
Look for the the bike the rides are defaulting to. Hover your mouse pointer to the right of it, and an "un-retire" link will pop up.
Once you've un-retired the bike, you'll be able to edit the bike and remove any defaults. Then you can go ahead and retire the bike again.
Give that a try and let us know if you have any questions.