I recently donated $5 (keep up the great work guys, great site) and now I have a 4/2 store overloaded. The bots won't let me add items either, dispenser 62 isn't overloaded either.
To hazard a guess, I would say it's because of my existing "Beta Tester" tag conflicting with my "Basic" level and removing my store slots. But no matter, if you could look into this and provide a fix that would be great :)