A call sign at the end of the line of a (new) rule indicates that it is overwritten by a previous rule. To resolve this conflict, the order of the rules must be changed. The rules you have just created must be moved up to be applied automatically.
Clicking the up arrow moves the rule up one line (see figure 1)
Figure 1: Ranking of rules
In figure 2 you can see the moved rules.
Figure 2: New ranking of rules