Layer 1 : Paint ; Layer Alpha to Selection
Layer 2 above: Wet Paint - Sample current and Below; Paint
From then on….
Whichever of those two layers is active - and
i) wet paint brush is active tool and set to Current and Below
ii) Selection (existing or new) applies (whichever View state)
….then content on that Layer vanishes.
Still exists on Layer, but is not visible if any of these conditions apply.
Problem does not apply to exported .pdf, nor .artstudio sent to Desktop AsPro.