Here's a quick tip in building KDE apps when you are not sure of what the prefix is. Instead of passing an absolute prefix to the configure script, pass the following instead:
--prefix=`kde-config --prefix`
Thanks again Headacher, but using #./configure --prefix=`kde-config --prefix` does not change anything, I get exactly the same error, looking again for KDE libraries in /opt

running amarok installed from Slackware12 package (using gslapt) :
root:# amarokapp
amarokapp: symbol lookup error: /usr/lib/libkhtml.so.4: undefined symbol: _ZN9KLineEdit17mouseReleaseEventEP11QMouseEvent
I got some very similar errors with the kdebase and kdelibs currently in the 5.9 repo's. I got me the kdebase and -libs from slackware 12 and now it's working just dandy. I'm not sure what's up with the ones in our repo, but I think they're faulty.
Can you check again with the kdebase and kdelibs in the repo to make sure we have them fixed?
I just tried KDE base package from VL testing repos (3.5.8-i586-4vl59) and get absolutely same errors. Impossible to load amarok, using the package provided in the same repo :
root:# amarokapp
amarokapp: symbol lookup error: /usr/lib/libkhtml.so.4: undefined symbol: _ZN9KLineEdit17mouseReleaseEventEP11QMouseEvent
Amarok splashscreen appears for about half a second...