Yeah, unfortunately it does look as though those (date picker) fields are being ‘hijacked’ by the selectbox script, which is enqueued by your theme.
We could definitely meet you half way here – this script, if added to your theme’s functions.php – can potentially get rid of that particular effect and targets only the submit events page: the catch is that you will need to figure out the name of the selectbox script handle.
For that I’d suggest going back to your theme vendor and asking, “What is the script handle used to enqueue selectbox.min.js?”
Supposing they tell you it is simply selectbox (and perhaps it is – you could certainly try that and a few other likely combinations out) then just replace the code in that snippet reading:
$handle = 'select2-handle';
With:
$handle = 'selectbox';
I hope that helps to resolve at least one of these issues 🙂