In my drop-down menu, I got 212 as my reputation, but in my profile, it is recorded as 203. Is this a bug, or is this deliberate? What makes these reputation counts different?
The dropdown counts are net changes, so the net reputation change for each time period listed.
The profile however lists all voting activity in that time range, so deleted votes (from those reversing their vote, or deleted users for example) won't show here...but their deletion will affect your net reputation, which the dropdown shows.
As an example: let's say you got a vote on Tuesday, then you later edited post someone didn't agree with on Thursday, so they take back their upvote. On Thursday you now have a -10 net change, but really it's because it's as if that upvote never happened, because it was retracted, this is where the profile and popup can differ.
If this bothers you, up to once a day you can trigger a recalc of your reputation at the bottom of your reputation report, here: https://english.stackexchange.com/reputation