In MATE (at least as shipped with Ubuntu 17.04), by default, Ctrl-Alt-{Left/Right/Up/Down} switches workspaces. Thus this shortcut is unavailable in applications.
In the "Keyboard Shortcuts" (mate-keybinding-properties) application, this shortcut is not listed. (Probably because it is handled by the underlying window manager Marco.) How can it be disabled?
You can use:
gsettings set org.mate.Marco.global-keybindings switch-to-workspace-left disabled
gsettings set org.mate.Marco.global-keybindings switch-to-workspace-right disabled
gsettings set org.mate.Marco.global-keybindings switch-to-workspace-up disabled
gsettings set org.mate.Marco.global-keybindings switch-to-workspace-down disabled
The names of those (and many other) settings can be found here (in somewhat unreadable form): https://github.com/mate-desktop/marco/blob/master/src/org.mate.marco.gschema.xml. The command for changing shortcuts is described very shortly in https://github.com/mate-desktop/marco/blob/master/README.
It may sound silly, but the keyboard shortcuts for switching between workspaces are available only when using more than one workspaces. I had to add an additional workspace from Workspace Switcher in Panel and then it was possible to disable the shortcuts from System->Preferences->Hardware->Keyboard Shortcuts
In general, to find out which keybindings are used by mate gsettings can be queryed.
Example listing keybindings for workspace:
gsettings list-recursively org.mate.Marco|grep keybindings|grep workspace
NOTES:
Control key also can be listed as Primary. ie:
org.mate.Marco.global-keybindings switch-to-workspace-left '<Primary><Alt>Left'
global-keybindings and window-keybindings, so to be safe change both.To disable a keybinding do a set for each one you want:
gsettings set org.mate.Marco.global-keybindings switch-to-workspace-left disabled
gsettings set org.mate.Marco.window-keybindings switch-to-workspace-left disabled
