randomly doesn't detect connected USB devices

[teo1978]

- A few minutes ago I had two USB drives (an external hard disk and a pendrive) connected to the computer. I opened Startup Disk Creator, and both USB drives were visible and selectable as target devices. I did nothing and closed Startup Disk Creator
- then I ejected and unplugged the pendrive (only)
- I started Startup Disk Creator again
=> expected: the still-connected external hard disk should be listed as a target
=>observed: it wasn't
- I plugged in the usb pendrive
=> expected: it should have been detected and appear in the list of available target drives
=> observed: it didn't
- then I restarted Disk Creator (at this time, both the usb devices were connected)
=> expected: both drives should be visible
=> observed: none is.

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: usb-creator-gtk 0.2.67ubuntu0.1
ProcVersionSignature: Ubuntu 3.19.0-32.37-generic 3.19.8-ckt7
Uname: Linux 3.19.0-32-generic x86_64
ApportVersion: 2.17.2-0ubuntu1.7
Architecture: amd64
CurrentDesktop: Unity
Date: Sat Nov 14 18:54:40 2015
InstallationDate: Installed on 2013-10-11 (764 days ago)
InstallationMedia: Ubuntu 13.04 "Raring Ringtail" - Release amd64 (20130424)
SourcePackage: usb-creator
UpgradeStatus: Upgraded to vivid on 2015-08-15 (90 days ago)