@dismine and @fabrice I have finally stumbled on a fix for an annoying problem I have had with valentina since I started using it on KUbuntu. The problem was the persistent warning Invalid URL: QUrl. whenever I tried to save anything to a new filename.
It turns out (at least in my KUbuntu installation) that it is not a valentina problem, which I knew. It is not a Qt problem either. It was related to the installation of the SAMBA package, which will probably be slightly different in each flavor of linux desktop.
After reading on the KUbuntu forum about a different problem, I investigated and looked at https://www.samba.org/samba/docs/man/manpages-3/pam_winbind.8.html
The fix was that libpam-winbind was not installed.
I installed it and used the following to verify that it was installed:
apt-cache policy libpam-winbind
After this, I no longer see any error messages reported in Valentina about "Invalid URL: QUrl"
I am posting this because it may be useful to other linux users of Valentina and may save @dismine time in trying to respond to those questions