Try changing the associations using Adobe Bridge's Preferences > File Type Associations.
Does not help. I also use the Prefpane "DefaultApp" but even the settings in there get resetted by some invisible hand from Adobe. Even if you don't have any Adobe app active, including Bridge login loader etc. You can't change CS5.5 claimed extensions to other programs. I'll zip the 5.5 applications and see what happens then.
If I zip the apps, then the previous programs are re-linked again. If I unzip InDesign CS 5.5 or PS CS5.5 again and run it once, all extensions are claimed back to CS5.5. Pretty anoying. How to kill this super-tight extension claiming of CS5.5?
Are there assosiation-lists inside the app package contents? Can I remove those if they exist?
In Bridge/file type associations what does the default setting say for .psd?
It now says Adobe Photoshop 8.0, but the Finder keeps opening psd's in PS 12.5
This won't help, but I can tell you that your problem does not happen to me with Ps CS5.1 and CS6 on OS X 10.6.8. I can set (via Finder's Get Info) all PSD to be opened by another app and that persists when both Ps and Bridge are launched and quit a couple of times.
What version of OS X are you using?
I use 10.6.8 as well.
Weird thing is, I only have ID and PS from CS 5.5 installed, yet .fh10 files are redirected to my old Adobe CS 1 Illustrator.... since the installation of CS 5.5!
I do have the preference-pane DefaultApp installed, but that is supposed to lock apps on a certain extension. It might conflict this time. I'll try to uninstall it once.