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When EE first came out, A-nodes stopped working as expected. (version number needed here)
You could get around this issue by adding any other one mesh in front of the thing you wanted to become transparent. For example, under your A-node, you would put another dummy, and adjacent to the dummy in order you would put your transparent mesh.
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A-nodes stopped working altogether. Static objects could no longer become transparent to dynamic objects without fail. (version number needed here)
EE Changes to Minimum Opacity and Discard Calls
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