I have an external USB soundcard. I use pavucontrol to route the audio to this
external soundcard (for each application)
but when I reboot this setting is lost, the internal soundcard is used, and if
I want the audio to be sent to the external
soundcard I have to select it again with pavucontrol. I'm using KDE, I'm not
sure if this is related, but in the KDE multimedia
settings I have a similar issue: I put the USB soundcard on top of the
preference list, but upon reboot the internal soundcard
goes on top. If I just logout and login again to KDE my preferences are not
changed, but if I reboot the issue occurs.

I have reported this issue on the pulseaudio mailing list:

http://lists.freedesktop.org/archives/pulseaudio-discuss/2015-May/023867.html

I have resorted to blacklisting the snd_hda_intel module to effectively disable
the internal soundcard so that the only soundcard
available is the external one and I don't have to select it through pavucontrol
each time.

I am also experiencing this bug. My device settings are lost after each reboot as Samuele mentioned, and I am also running KDE. I've noticed that on each reboot, pulseaudio is creating another set of config/tdb files in ~/.pulse/
I have attached the output of ls -lh in that directory to illustrate this. Also attached are my ~/.pulse/daemon.conf and /etc/pulse/*.{conf,pa} files.
My installed version of pulseaudio is 5.0-13_amd64 running on Debian Jessie.

Regards,

Ben Reedy.