Hi Gerardo,
This default setting is a bit confusing, since it only defines a default, if no tab-state tiddler exists.
This state tiddler is automatically created, as soon as you select a tab. Then the state is saved between sessions.
So at the moment it's not possible to reset the sidebar tab state, out of the box.
Can you tell us, why you want to reset the sidebar tab on reload?
----
There is a setting, that should allow us to exclude certain tiddlers from being saved. eg: sidebar state, ... but ...
I did have a closer look at the core code and found some inconsistencies. I'll file an issue about this at github.
-mario