Thanks, Maggi. Those are great photos you found. Looks convincing...
I was wondering about the sticky stems under the flower on this plant. Another plant I have that has been tentatively ID'd here as Saponaria x suendermanii (sp?) is also sticky around the upper stems and inflorescence, so perhaps this is not unexpected for Saponaria.
Edit: By the way, I also got Saponaria x suendermanii (sp?) as a supposed Saponaria lutea, same as what this plant was supposed to be! All this made me very curious to see what the heck Saponaria lutea actually looked like... and I did manage to end up with the real thing in my last attempt!