I will test this myself, but it could be that condenser is using your owner key in the browser. All of your keys (owner, active, posting, memo) are derived from the master password, so it's possible that condenser (the steemit.com webapp) just uses owner by default for everything, which would explain this behavior.
Please file an issue at https://github.com/steemit/condenser/issues/new to begin a discussion about this issue. We'll track it down.
Best,
-jp