Have Rich Teas got weaker?

I only ask because I pride myself in knowing the magic dunking time for most biscuits. But (and it's doing terrible things for my self-esteem), twice in as many days have I lost a signficant portion of a rich tea into my cup of hot brown. Granted these are the Spar own-brand variety as opposed to the Rich Tea standard that is McVities, but I assumed that, like computers, shampoo and cars, they're all pretty much made in the same factory anyway.

So the question is, have the universal Rich Tea manufacturer (lets call him God) changed the recipe so that the O.D.T. (Optimal Dunking Time) has been radically altered?

Or could the fact that thes ones I have are half-chocolate-covered and that's what's making the difference? Damn, that's a whole new calculation.

And to prove that I'm not the only one worrying about this life-changing issue...