I'm not sure if this applies or not (taking a guess), but some shaders materials don't always show well depending on what preview mode the staging room is set too and what the settings for that are. I'd say to paint with one that doesn't seem to show, and test it with the preview tool. (The camera icon thing that lets you drag a box.) If the texture shows properly there, then you're probably ok.

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Barbequed Pixels?

Your friendly neighborhood Wings3D nut.
Also feel free to browse my freebies at ShareCG.
There might be something worth downloading.