I have to correct myself: I didn't restart my KDE session so I guess the old libmtp was still used by the KDE daemons. After a new logon, mtp-detect works fine!
This might also explain why the quick-connect hack worked (just guessing): If I was quicker than the KDE daemon (whichever that is) I was able to grab the phone with new new lib, else the old version would have mis-initialized the device.
I have to correct myself: I didn't restart my KDE session so I guess the old libmtp was still used by the KDE daemons. After a new logon, mtp-detect works fine!
This might also explain why the quick-connect hack worked (just guessing): If I was quicker than the KDE daemon (whichever that is) I was able to grab the phone with new new lib, else the old version would have mis-initialized the device.