Shield Bash?!

Okay if this is all common knowledge and something everyone else can do I apologize in advance.

I was farming chunks in Kiln earlier and after the 2nd BK I stop on the stone bridge (going sideways) I switch my Black knight shield to the Black bow of Pharis, fire off an arrow to aggro (Don't want my precious product to fall now) I quickly switch the bow back to the shield and...
See my character do a Left handed shield bash identical to the ones Black knights do. It wasn't the same as when it's in the R slot, but exactly like NPC's do it. The whole, tilt sideways and shove forward. I did it 3 times too so I was sure it wasn't something else.

My question is: What triggers this?! I have only done it on that ledge before the bridge after shooting the Black knight, and once in front of 'Santa the Blacksmith' (first sighting but I thought I was just seeing things) so have I found a new thing or is this all old news and I'm just being n(ew/oo)bish?

I think it's a code glitch, I've seen it happen several times but I have never been able to do it on command to tell if it is an actual shield bash.

My pattern was (Without the whole story):
Change shield to bow
Shoot bow and hit enemy
Quickly (~1 seconds) switch back to shield
*Shield bash*

Although when by Santa I didn't shoot the bow and it did it anyways.

That's exactly how mine have occured, I'm still unsure what is causing it to happen randomly though.

It happened to me a too a long time ago, but it was just once. Also it was cool as hell! The Black Knight blocked my shield bash and I break his guard! IN ONE HIT!

This has happened to me if I block/parry (can't remember) right after I lose lock-on, character might have to turn as well. I could be mixing this up with another action.

It looks like there are more moves tied to weapons than what we have buttons for. I was also fighting hollow reah and she could block with her left hand, but we can only punch or parry. I originally thought they had tried to implement a 'leftie' choice during character creation, because of the shield bash, but that theory is out the window if it's different from the right hand bash.

Thinking about it, I would really like the option to make left handed characters, it could add some surprise and diversity to builds.

Definately, but it would be bad since shields would have to be changed, a Right hand shield can't block a left hand sword as easily. And vice versa.
(I'm not saying it's impossible but it just seems more awkward to do.)

happens to me quite often actually, right when im in a "if i *** up im dead" situatuion where i need full concentration to survive

such as fighting a black phanton titanite demon...