I have seen this
A long time ago (1997) this happened several times in different organisations. Caching web gateways set wrongly and cahing the page without any reference to teh query string or form variables.
Really nasty but easy to fix.
A security snafu on YouTube allowed users in the UAE to view the account pages and preferences of other users. The bug also created a means to jump into Gmail in cases where surfers had linked their YouTube and Gmail accounts. The issue appeared to only crop up locally, within the UAE, and only for users of the Etisalat …