I'm currently volunteer propagating for a grower that specializes in the "less-than-common" as it's "that time of the year" and I have a few that I can't seem to figure out what the secret is to getting cuttings to take. One that I have never been able to get to go is Argyrocytisus battandieri http://davesgarden.com/guides/pf/go/1702/ . The cuttings are soft and the foliage flops so quickly.
The other is Romneya coulteri http://davesgarden.com/guides/pf/go/2504/ - cuttings just don't seem to take no matter what I do. Any suggestions are appreciated.
I haven't had any experience growing either of those plants from cuttings, but I have developed techniques for growing zinnias from cuttings, and some of those techniques might solve the problems you have encountered.
"The cuttings are soft and the foliage flops so quickly."
Conventional cutting methods with zinnias fail in the same way, because the zinnia stem and leaf tissues are very vulnerable to bacterial rot, and they lose water through evaporation from their leaves and collapse long before they have had time to strike roots.
I use diluted Physan 20 to sterilize my cuttings and the water that they are supplied with. I use a good rooting hormone like Dip 'n Gro, which has two different rooting hormones. And I keep my cuttings under fluorescent lights under a humidity dome for up to 10 days to give them time to strike some roots. The Physan 20, rooting hormone, fluorescent lights, and humidity dome are the prerequisites for success with zinnias from cuttings. They might help with your problem cuttings.