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I have not heard of this exact issue but I have heard of weird things happening when people get tricky with Geo location sniffers. I strongly suspect it's a setup issue though I'm not sure what exactly. If I were you, and if at all possible, I would kill all caching and the http accelerator so I could determine what's real. Give it at least 72 hours to purge. Then you can turn things back on one at a time and test as you go.
I'd also check robots.txt, htaccess, and look for any caching files from the old plugin and kill them.
[edited by: lorax at 7:09 pm (utc) on Apr 22, 2014]
[edit reason] typo [/edit]