The behavior of SPICE USB redirection has changed when redirection is disabled.
From the dev bug 1373223:
If SPICE USB redirection is enabled (VM-like dialog > Console > USB Support), the behavior remains unchanged: each VM has a quadruple of usb controllers: ich9-ehci1, ich9-uhci1,ich9-uhci2, ich9-uhci3.
If SPICE USB redirection is disabled, then VM has newly USB controller as specified in osinfo-defaults.properties configuration file, i.e. it is configurable per guest operating system and effective cluster version. Previously no usb controller was send to libvirt and libvirt created a default usb controller.
Default for all intel (x86, x86-64) operating systems is "piix3-uhci", for ppc64 systems it is "nec-xhci".
SME feedback from Jakub Niedermertl about the 'USB Support' field in the 'Console' tab of the 'New Virtual Machine' window:
Despite the name this dropdown controls spice usb redirection.
Enable: spice usb redirection is enabled allowing client to attach his/her usb device to a guest VM. VM is added special set of special 4 usb controllers.
Disabled: usb spice redirection is disabled, USB controller devices are added according to "devices.usb.controller" key in "osinfo-defaults.properties" configuration file.
Moving to 4.2.