I seriously doubt it is a sport. A sport usually only happens in a cane or a lateral. That means the cane would be uniformly variegated while the rest of the plant would stay healthily green. Variegated leaves caused by a sport should not have malformed growth. On what grounds does the rose nursery claim it's not a disease? I rather suspect it is, because with out them knowing more; like there unknowingly has been propagated a sport of Sentimental in their fields, or these plants have been tested for virus it is unlikely they have any ground to their claims. On the other hand it doesn't have to be virus. There are a number of causes other than virus that have been listed by posters in this thread. If there have been trouble with virused roses the nursery probably knows about it. If it is some kind of problem with absorption of nutrient, there is a pretty shore test you can do. Buy a type 100 % water soluble fertilizer (the Miracle Grow type) with all NPK and trace elements, preferably double the amount of kalium than nitrogen. Water the plant with this regularly, like two three times a week. Every fourth of fifth watering can be with weak solution of calcium nitrate (pure calcium bound nitrogen). This will show on the plant within a few days, and within a couple of weeks even badly clorotic leaves will improve dramtically, if not always entirely. New growth will be all fine. If this treatment results in healthy clean growth you can be pretty shore it is caused by lack of nutrients, or at least something blocking the nutrient absorption. The side effect of this treatment is roses very badly prepared for winter so it's really not a good idea in areas with frosty winters, at least only in spring / early summer. Action needed to be taken; dig up rose and improve soil with appropriate amendments. If this has no effect on the plant, you know it isn't caused by nutrient deficiency. If you can find traces of bugs that have been sucking on buds and new growth, they can give symptoms not unlike these. Then there should be tiny puncture holes some where, and the insects are a bit difficult to define; there is lots of different ones, belonging to the Heteroptera family. At least you should find some of the sinners jumping or flying around your roses.

Was at L's yesterday trying to buy wood-crafting tools they don't even sell (go figure!) and the few TC's left were on clearance. The $10 were $5 and the $3 plants were .50. Although there were several bigger ones with white, very white flowers, even I couldn't rationalize such a purchase with the present-budget. So I got 7 little .50 ones with the lightest colored buds. For $3.50, worth waiting for a year to see what they open to, assuming all of these buds will fall off as I'm expecting. I also picked up all of the broken pieces from the floor & stuck them in the tray. A few look promising, and total mysteries regarding flower color. Now, where in the world am I going to put these things? I'm pretty sure I'll be cutting more/bigger holes in the sides of hanging baskets & sticking them in those. Seriously no room for any more pots!

You'll notice in Photo # 3 when she walked up to the thing that it looks like she's giving that look of "this is the car I want" DAx ;)

I'm going to bump this down.