On automatic update of plugins, the activation hooks are not executed.
This results in the fact that required updates of db tables are not performed and therefore the generation of run-time (sql) errors.
The plugin developer (me) assumes de-activation before and re-activation after a plugin upgrade.
A workaround is to have my own 'db revision level' and checking it in every admin page of the plugin and run the required routine then.
Leaves us with errors when this has not been done yet.
Is the ommission of running the (de)activation hooks a feature or a bug? To me its a bug.