Version: 1.9.6 (enterprise 20070904.708012) (using KDE 3.5.7 "release 78.1" , openSUSE )
Compiler: Target: i586-suse-linux
OS: Linux (i686) release 220.127.116.11-0.5-default
IMHO these functions should be "complementary" in case the result is false
open the address - if "address not in addressbook" - option "add to addressbook"
add to addressbook - if "address already in addressbook" - option "open addressbook"
BTW this is especially important in companies where common addressbooks are used hence the single user does not know if an address is already in the addressbook.
I committed this exact solution yesterday.
The fix will be in KDE 4.1.4 and KDE 4.2.0