KDE Apps extensively use KIO objects which can also do network communication. So when you write a KDE Apps you don't have to worry much about network programming. It may be that these KIO Objects block the KDE Apps for the timeout time for network accesses.
As I said: It may be...
Each start of a network access can have up to two states:
1) Do a DNS-Query to convert it into an IP-Address/Network
2) Connect to the desired device/Do network scanning, etc.

1) and 2) can block apps. So when network is not configured correctly apps can be blocked for a while. You can see this when debugging with strace, gdb, etc.

Cheers, Martin