We have a bunch of Phonegap apps that haven't been updated since March 2014, so I've just repackaged them all up and uploaded to Phonegap Build. Very impressed so far - doing away with the labour of managing local Phonegap installs and SDK's is truly amazing!
Phonegap Build wouldn't accept my key.jks file though, so I renamed it key.keystore and this then uploaded fine. I gave it the same alias and Phonegap Build compiles the APK's successfully with it. Alias and passwords haven't changed - literally just the filename extension.
When I've come to uploading the compiled APK's to Google Developer Console though, it's rejecting them because "You uploaded an APK that is signed with a different certificate to your previous APKs. You must use the same certificate."
I can only assume that either the filename change is causing a problem, or Phonegap Build is doing something during signing. Either way I seem to be a little stuck!