Flag name conflict is reserved for cases where different flags are set for the same element, and their properties cannot be merged without loss. For example, a conflict occurs when two such flags are both assigned the same color property but with different values; or when the value of fgcolor is the same as the value of bgcolor, either for the same flag or for different flags that apply to the same element.
Probably you would want to assign noticeable properties to the conflict flag, so the problem stands out. For example:
[ConditionalFlags]
conflict= bgcolor=white fgcolor=#ff00ff overline underline