Inserting USB cable connected to Android Phone causes full system freeze

[Phill]

Specifics of the conditions, although these may not be relevant as this configuration has been working and still works intermittently:

USB Cable is already connected to the computer via extension ports.
Phone is switched on and screen unlocked.
Cable is then inserted into the phone.
Phone is an HTC One M8 running Cyanogenmod 12.1, root not enabled, ADB not enabled (although android utilities are installed on the computer).

System completely freezes on clicking the device icon in the launcher, with video and mouse pointer frozen, terminal switching doesn't work, no disc activity showing. Tried again after reboot, same happened. It does work sometimes.

I have not tried an alternative cable or port as I wanted to get this reported before being forced to reboot again.

I've report this bug, regardless of what I might find subsequently on testing cables and cleaning the USB ports, because I think that the system should at least survive in the face of such problems.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: linux-image-3.16.0-70-generic 3.16.0-70.90~14.04.1
ProcVersionSignature: Ubuntu 3.16.0-70.90~14.04.1-generic 3.16.7-ckt25
Uname: Linux 3.16.0-70-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.19
Architecture: amd64
CurrentDesktop: Unity
Date: Fri May 6 15:13:26 2016
InstallationDate: Installed on 2015-07-13 (297 days ago)
InstallationMedia: Ubuntu 14.04.2 LTS "Trusty Tahr" - Release amd64 (20150218.1)
ProcEnviron:
 LANGUAGE=en_GB:en
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
SourcePackage: linux-lts-utopic
UpgradeStatus: No upgrade log present (probably fresh install)