I had similar problem about 1/2 year ago - anything faster than 1/30 was displayed as a mess (everything lit up).
I took a good screwdriver, carefully unscrewed the 3 top screws, lift the whole LCD assembly up, then I disassemblef it from bottom, and again put it all firmly back to it's place - and whoa, it work ever since then like new. so I think it might be a case of bad contacts.