Upgrading from 50/34 to 50/39 with Shimano Sora? I have a road-biased hybrid that came with a compact 110mm BCD 50/34 Shimano Sora crankset and chainrings. I'd like to upgrade the inner ring to 39, but I'm having some trouble figuring out what to buy. 

I initially picked up a Vuelta 39T "flat" model, but I can't get a clean shift from 50 to 39; the chain slides into the space between the rings, then floats on top of the cogs in the bottom ring, before finally meshing. This occurs when I'm at around 20T or smaller in the rear, regardless of how I've adjusted the front derailleur. The stock 34T Shimano chainring seats immediately. Somehow the Vuelta cogs never seem to line up properly when the chain comes down. 

Do I need to replace both chainrings? Or do I need a Shimano model of the 39T? If so, from what generation (e.g., would a from chainring designed for an 11-speed chain still work with this 9-speed Sora?)? Shimano's compatibility chart seems not terribly helpful for this one. My current plan is to upgrade the whole crankset to a 105 5800, but I'd rather not if I don't have to.
Take a look here http://www.vueltausa.com/components/chainrings.html
It looks like the flat series is for single speed or old style 5 or 6 speed non indexed shifting bikes.

Suggest you need the SE Plus range http://www.vueltausa.com/components/chainrings/se-plus-chainrings.html which is designed for 7 to 9 speed. It should be narrower than what you have, which may be why the chain is fouling.