Double check your pushrod adjustments, to be sure that they are not too tight.
Adjust them when the engine is cold, and have no perceptible up/down play, but NEVER too tight. They should easily spin with finger spinning when cold.
The mechanics in India are notorious for setting pushrod adjustment too tight, in an effort to make the bike quieter. This is VERY bad and should NEVER be done.
Too-tight adjustment of the pushrods can cause this kind of spitting back, in some cases. I'm not saying it IS causing it in your engine, but it should be checked, especially if any Indian mechanic had his hands on it.