On several occasions I found myself unable to "cancel" the use of the following special items: binoculars, rocket launcher, sniper recon grenade launcher.
As you can see, they all have in common, that you not simply consume or throw them on use but activation will trigger a change of view/perspective (similar to entering scope mode).

If I remember correctly it happens like this:
a) in the item wheel I switch to one of the above mentioned "special items"
b) I press "G" to "use/activate"
c) I decide against usage without firing and press right mouse to "cancel"
d) but cancellation does not really happen, instead you are rendered helpless.

In detail the results are:
- I can't shoot or switch any weapon. (left and right mouse buttons without any reaction)
- I can move but not go prone.
- I can't interact with anything (cars, keypads, intel items).
- I can't change the active item via the item wheel or any other way.
- I can open menus, map etc. but I can't fast travel

Only option is to log out / return to desktop.