ConditionalFilter never uses C code for AveragePlane?

[ChiDragon]

Looking at the source for 2.5.6, it appears that ComparePlane assigns a bool called ISSE and decides whether to use C or ISSE code, but AveragePlane just throws an error if it detects a CPU incapable of integer SSE, even though there is a C function written:

if (!(env->GetCPUFlags() & CPUF_INTEGER_SSE))
env->ThrowError("Average Plane: Requires Integer SSE capable CPU.");