We are all very happy to see the Mango release, and up to this point the upgrades have been going incredibly well for Microsoft's first major upgrade to the Windows Phone platform. However, there have been some reports (on the XDA Forums, Twitter, etc) of some onscreen keyboards disappearing. There have been reports from other sources stating that it doesn't to be a device specific issue. There also have been some mobile phone authorities mentioning that this issue was existent in the beta Mango release, and is still not fixed.