if you use knetworkmanager as your mentioned KDE Network Manager, restarting the networding script cannot work:
The script does only handle network devices that are configured in /etc/network/interfaces (on debian an related distributions - others might have a coresponding file somewhere).
The knetworkmanager does only manage devices that are _not_ listed in the interfaces file mentioned above. This is usefull for mobile network devices - like your wlan device.
Both ways to configure network devices work complementary.
If my WLAN hangs, I usually reconnect the device using the knetworkmanager GUI (translation could differ, I run no english system):
1) Right click the icon
2) Select "Options"
3) Select "Change to offline modus"
Wait until everything is disconnected
4) Repeat 1 and 2, select "Change to online modus"
Wait until everything is reocnnected.
Perhaps, you have to select your WLAN manually after changing towards online modus.
Hope this one helps,