segfaults in most KDE apps; KDE5 wont start (regression)

[Dave Gilbert]

KDE5 won't start for me today, and there are segfaults in dmesg (XFCE is running fine):

dg@davros:~$ dmesg|grep -i segfa
[ 17.799106] ksmserver[1075]: segfault at 1c496 ip 000000000001c496 sp 00007ffd3a4e00a8 error 14 in kdeinit5[400000+d000]
[ 20.514638] kactivitymanage[1084]: segfault at 7f04e814ecd0 ip 00007f04e8104261 sp 00007ffcdb4d76e8 error 4 in libQt5Sql.so.5.5.1[7f04e80f0000+3f000]
[ 28.805973] ksmserver[1294]: segfault at 1c496 ip 000000000001c496 sp 00007ffcf92fa528 error 14 in kdeinit5[400000+d000]
[ 29.379577] kactivitymanage[1296]: segfault at 7f840801bcd0 ip 00007f83fc0dc261 sp 00007ffe90b0a7b8 error 4 in libQt5Sql.so.5.5.1[7f83fc0c8000+3f000]
[ 40.320441] ksmserver[1507]: segfault at 1c496 ip 000000000001c496 sp 00007ffeb35f10f8 error 14 in kdeinit5[400000+d000]
[ 40.837963] kactivitymanage[1509]: segfault at 7fab181bccd0 ip 00007fab18172261 sp 00007ffe525e6968 error 4 in libQt5Sql.so.5.5.1[7fab1815e000+3f000]
[ 391.681422] ksmserver[2606]: segfault at 1c496 ip 000000000001c496 sp 00007ffd98e084c8 error 14 in kdeinit5[400000+d000]

This is a machine that's on Xenial having been upgraded to the alpha a few months ago. A couple of weeks ago the KDE panel stopped appearing/but I didn't have time to report it. As of today the desktop doesn't start
and I'm returned to th display manager. I've done an update today and it still doesn't play ball.

I tried wiping .kde/cache* and it didn't help.

Dave

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: kinit 5.18.0-0ubuntu1
ProcVersionSignature: Ubuntu 4.4.0-10.25-generic 4.4.3
Uname: Linux 4.4.0-10-generic x86_64
ApportVersion: 2.20-0ubuntu3
Architecture: amd64
CurrentDesktop: XFCE
Date: Sun Mar 20 13:14:20 2016
InstallationDate: Installed on 2015-12-25 (85 days ago)
InstallationMedia: Ubuntu-Server 15.10 "Wily Werewolf" - Release amd64 (20151021)
SourcePackage: kinit
UpgradeStatus: Upgraded to xenial on 2015-12-25 (85 days ago)