I commonly subscript the terms object in the survival package, most often to remove "cluster" or "strata" before calling model.matrix. This action removes the dataClasses and predvars attributes.
I have special code to work around this at the moment, but it would be useful if these were retained. I'm currently fixing a bug in survfit.coxph whose root is an error in my workaround.
At the least we need a reproducible example, and a patch which does what you want would increase a lot the chances of getting this fixed the way you want.