Hi Glauber,
Yes, this helps and it makes perfect sense now. :8} Thx a lot!
The description for <check-valid-connection-sql> somehow misled into believing that it also implicitly turns on the validation and that background-validation = true in turn implicitly changes the semantic. Something like "an sql statement that is used for validating the connection. Validation can be triggered on every connection check-out (default; see <validate-on-match>) or/and asynchronously in the background (see <background-validation>)" would be much more helpful.
Again, thx for help.