Sharraxaadda

Traveling southbound on 11th St NW, the speed limit changes three times in three blocks. It's unposted (25) until the 1300 block where it goes to 30. Then it drops to 25 in the 1200 block before going back up to 30 in the 1100 block with a tiny little speed limit sign. Why does the limit change so much and should it?