My problem with DAP DYNAFLEX 230 caulk

I've been using and recommending DAP Dynaflex caulk for many years -- since it was called Formula 230.  I like it because it remains flexible for a long time, preventing cracking along the sealed seam.  But, I must now face the fact that is seems to be an aggressive growth medium for mildew. 

In the following pictures the dark/black caulked areas are mildew -- not grime.

In each case when I rework the seam, I scrub it with a toothbrush and TSP solution.  I follow this with a bleach solution.  I then prime the area with Zinser Bulls Eye 123 primer, and top it with two coats of Pratt-Lambert Accolade.  All in an attempt to prevent the mildew coming back.  But, to no avail.

The seam in this next picture has been redone three times (making a total of 4 times including the original).

The following seams have been redone twice

This seam is a caulked vertical joint between two 4x8 pieces of exterior wall paneling

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