Two possibilities to check:
- A custom menu may have omitted the corresponding menu options.
- A restrictive option in "Available Menu Commands" for the user's privilege set may omit the corresponding menu options. (See Manage | Security.)
Either way, when the corresponding menu options are made unavailable, the corresponding keyboard short cuts and context menu options are also unavailable.
The second scenario was it. I thought I was simply limiting the options of editing layouts etc. and wasn't aware that it also stopped the right click from working properly.
As always, thanks Phil!!!