Let's take the following deterministic example where Z is an Exclusive Or between X and Y, i.e. true when X and Y are different.
The analysis of the relations with Mutual Information (Validation Mode: Analysis | Visual | Arcs' Mutual Information) returns the following graph where the mutual information between X and Z and Y and Z are both null.
Indeed, X and Y do not have any impact on Z when they are analyzed separately.
On the other hand, the force of the arcs computed with KL (Validation Mode: Analysis | Visual | Arc Force) reflects perfectly the deterministic relation between of X and Y on Z.