As I said on Twitter :
Pics (plus a video of Gabe Newell confirming) or it didn't happen.
You are sickening me Michael.
Your gaming news are garbage.
This isn't even news ! What is this shit doing in my RSS feed ? F*** you !
Plus, how come you receive an email from Gaben though you don't have Valve's favors ?
Valve is silent enough when it comes to talking about their next games, & evasive when giving a release date...
Some drivers will recompile shaders under specific conditions, for instance when a uniform value becomes 0 or 1, in order to eliminate noop expressions (e.g. add 0), eliminate conditionals, reduce register pressure and total instruction count.
Nvidia used to be very aggressive with such optimizations back in the geforce 5 and 6 days, much to the annoyance of game developers. Typical workarounds include small epsilons (e.g. 0.001 or 0.999) or multiple side-by-side shaders that are bound depending on uniform combos.
As gpus got more complex, these optimizations became less prevalent, but it could very well be that some drivers might still use them.