> The issue is that every driver implementation ever ships with a slightly different implementation of that complex parser. That means (every mobile device)X(every OS update) and (every PC ad-in card)X(every driver update) all have the potential to misinterpret/reject your shaders in slightly different ways.

I can confirm this happens a LOT. (At least with ESSL) In it's defense, it usually is a mistake I made, but some implementations are definitely more lenient than others.