I have enabled the option Open as tab in existing Konqueror when URL is called externally (Settings>Configure Konqueror...>General) on Konqueror, but it does not opens the new web pages, that I call from other app (like Choqok), on a new tab, it opens a new window of Konqueror. Really this is a annoying behaviour for me, becouse I call always new URLs from Choqok and it uses too much resources of my machine (RAM memory).
Here is a screenshot of the general option on Konqueror:
I use KDE 4.4.4 and Konqueror 4.4.4 and Archlinux 2.6.33-ARCH
try: systemsettings -> default apps -> web browser -> click "in an application based on ....." -> apply
what you've checked opens middle clicked links in an existing Konqeror window in a new tab, else it will opens them in a new K window - the setting you're referring to is for the existing K window not for other apps opening links.