Terms added to node when they shouldn't

I've set one ccktssu field so that it works like a field: I left uncheck the "Add used terms as node tags?" box.

I added a term, thanks to the "Add a Term" widget on the node add/edit page ("allow freetagging at the top level of the vocabulary") to a node of the type where that ccktssu field is assign to, submitted, and saw it within the "link" div of my node's content, and the term within the vocabulary list associated with the node I created the term with.

The term, unless I misunderstood the purpose of the "Add used terms as node tags?" checkbox, was added to the node while it shouldn't have. I thought the term would have been created for the vocabulary, and then just picked up by ccktssu when needed, but not added to the node. Indeed, the normal behaviour should have been what's described under this option checkbox:

Normally, this module does not include selected vocabulary items in the node's taxonomy field, and therefore does not save anything to the term_node table. This prevents nodes from showing up in taxonomy term searches (...)

But I thought then that the reason may depend on the following case:

In this particular (and other) nodetype, I have two different ccktssu field for one vocab.

(May be badly translated, but should still serve the) Example:
- My vocab is "Dressing".
- I have one main ccktssu field called "Dressing artist". The term should be added to the node.
- I have another ccktssu field called "Dressing assistants". The term should *not* be added to the node. (This is on this field that the term has been added and therefore unexpectedly to the node too).

Thanks.