In the Airbus, you push (if I remember correctly) the Alt Set knob to switch to 1013.
When switching back to QNH, you pull and it'll display the last QNH set (usually the one from your Origin). Then you'd turn it to the new QNH.
On the CRJ, you have a "push for STD" function also, however there is no "pull", you simply turn from 1013 to set the new local QNH.
So without knowing for sure, it seems Airbus "remembers" the QNH, or has 2 Alt settings, one STD, one QNH running through it's guts.
And the (much simpler) CRJ just has one, which happens to be 1013 when flying levels.
Nic