I have an app version live in the play store, signed with my “old keystore file”. Now I gave my old key to Google, and sign the next version of my app with the “upload key”.
If I now manually (locally) try to update one of the old installed APK’s with my new APK, there is a conflict, the phone states: “another app conflicts with yours”; it does not recognize the new app as an update of the old app, probably because the keystore file used to sign this new version is different (and the package is the same, thus the error).
Is this normal behaviour for this one time? This will not happen if I now upload to the playstore and update from the play store (since Google will use my “old keystore” to re-build the app on their server)?
This is normal behavior. You cannot test this single update because the key changed from a normal build key to an upload build key. However, if you upload to the Play Store your update will work fine, since Google re-builds your project with the normal build key.
Test it out in beta though, to make sure there are no other issues with your update.