Protest message when no subs raiding

[havoc1371]

Why is my PBEM game having "US protests sinking of merchant ships" messages when the Central Powers has no ships or submarines currently raiding convoy routes?

[mdsmall]

Because there is a 4% chance per turn of triggering the U.S.and receiving that message if there is one CP naval unit within 50 hexes of hex 80,87. It does not matter if the naval unit is convoy raiding or not.