This is from "Cessna Wings for the World", by William D. Thompson,
regarding the C-177:

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The pitch-down motion in flaps-down sideslips was a more serious
problem, however. Production test pilots became aware of a more
noticeable waviness in some of the leading-edges of the wing, and
occasionally, a 2-foot length of paint overspray that caused wing-
dropping tendencies at the stall. This had to be corrected by
applying body filler material on the leading-edge or rubbing compound
to remove the almost invisible overspray. There was also questionable
uniformity of the stabilators, giving as much as 15-mph deviations in
minimum trim speeds. On some airplanes they reworked or actually
replaced the stabilator with some improvement. This led to the
decision to incorporate slots into the stabilators' leading edges so
that they could tolerate a steeper downflow of air without stalling
the under-surface of the stabilator. This solved the problem, and a
fleetwide "Cardinal Rule" retrofit was planned at no cost to the
customer. In the meantime, a service bulletin called for a temporary
installation of a simple sheet metal plate that would limit the
maximum flap deflection to 15 degrees. We were paying the price for
these thin skins.
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So this was more than just a stabilator stalling; it had more to do
with production problems than an inherent design problem. A tail-
stalling airplane wouldn't pass certification tests.