If you change the database properties via the admin console they persist.
If you undo the changes the old ones are still there.

For example

In the admin console

1) Select Datasource -> Local TX Datasources
2) Select DefaultDS
3) Select the Configuration Tab
4) Un check the Check Valid Connection SQL check box and enter any sql statement - like 'select * from dual'
5) Select Save - all saves fine

6) Select the Configuration Tab again
7) Un check the Check Valid Connection SQL check box - the box clears
8) Select Save - all appears to saves fine

9) Select the Configuration Tab again
10) Observe that the SQL statement is stiil there even though it was cleared in step 7.