Why did you create those symlinks?

Trying to get Flash to work.

Doesn't matter, I found the answer (see the edit above). I've got working 10.3 Flash now, and found that (as expected) a symlink works just as well as a copy of libflashplayer.so in the opt/flashplugin-nonfree/[version]/ folder. With that symlink installing, flashplayer-selector produces the expected changes and no longer gives the update-alternatives error it did previously.

Glad to hear you got it working.