Many many thanks to Flock engineers Erwan Loisant, Mike Dosik, and Patricia Bacon. They took time with me over the past few days to get my problem debugged and now categories worked. Here are the details in case you find yourself in my situation.
First of all, once they told me that it worked on WordPress blogs in general, I was starting to think that it might be a problem on my end. It turns out that it was a problem on my end! After some debugging, Erwan found out that Flock was getting back the message that the pulling of the categories was requiring more than the alloted 8 MB for PHP memory. So I went in and increased that and now it works!
So, thanks to the hard work they were willing to put in to fix this and the fact that I can now blog from within Flock, I will make it my default browser on Windows. Good job on winning me over, guys!
Blogged with Flock