I wish people would stop throwing "IT'S A BETA" to everyone who posts questions about bugs on here. Everyone here is aware that this is a beta, and everyone is aware that there are bugs. So how about instead of just saying "there are bugs on a beta", which is a waste of a post because it's an obvious fact, how about we offer help and suggestions on how to fix things in the meantime so everyone can have a better time using/testing/enjoying or developing on ios 7?
And now for OP: have you tried restarting/hard rebooting? If that doesn't work, maybe try resetting all settings - that'll get rid of all your settings including the wallpapers, but it won't delete any apps/data. And if that doesn't work, then either you can live with it for a while if you can tolerate it, or perform a restore.