It's my understanding that when you render to Flash, Poser makes a vector trace of your render (like a cartoon). I could be wrong, but I'm just about positive of that. If this holds true, then your only choice is to render the animation as an AVI or whatever, then convert it to a rasterized flash movie (non vector-traced) using some other Flash conversion software. There was a good one I used to have a while back, called something like "WildFlix" or some such name.

---

Tools :  3dsmax 2015, Daz Studio 4.6, PoserPro 2012, Blender v2.74

System: Pentium QuadCore i7, under Win 8, GeForce GTX 780 / 2GB GPU.