This does not always happen, but i had the same Problem while playing different missions!
You can normally solve the Problem by restarting the mission...
A bit annoying, but yes...
This issue is hard to reproduce, it just happens when you don't need it ;)

Clearly a downvote...
In the austrian army its taught just like that in arma!!
It gives you more stability when dealing with the recoil, just like crazydude said!
Experienced it myself, you can't See in a picture wheter it's like this or not...

Simply dont shoot the last rounds if they annoy you! Its realistic, its arma...

Go ask a modder...
I dont think that military will use crossbows in 2035... Downvote!