I have similar problem as you have. I also have notebook (Acer ASPIRE 5553G) with ATI mobility radeon HD 5650 and HD 4200 I believe. I tried to serach for drivers for this switchables graphics and I find http://sites.amd.com/us/game/downloads/Pages/downloads.aspx where I could download driver for 5650 and also 4200 legacy for W8. I was so happy that I finally found one. BUT here comes another bug.
When I installed drivers for HD 4200 it makes my HD 5650 disapper from Device manager and system acts like there is only HD 4200. The same problem appear when I install driver for 5650 but in this case HD 4200 was gone. = swichtable graphics wasn't able to switch anymore .
So at the end I was so mad that I decided to go to BIOS and change settings for graphics to use only HD 5650 (with this settings battery last only one hour so use it only when you are using cable), if you need laptop somwhere out where you cannot plug in it in wall simle go to BIOS change options for graphic to use "Switchable", in Windows install driver for HD 4250 that "beats" your HD 5650 and your laptop can handle about 3 hours, depends on your usage of course.
I know that this "solution" isn't perfect but I didn't find any better. Maybe wait for AMD support to make this problem disapper .
EDIT: ACER Aspire 5553G ; AMD Phenom II X4 Mobile ; ATI mobility Radeon HD 5650 + 4200 ; 6 GB ram ; W7 (problem was there) -> upgrade W8 (problem still here )