Spintax in post data

I’ve just been having a play around with some old engines, and noticed that SER doesn’t seem to allow spintax anymore when performing a ‘post data’ request. Example:

[STEP1]
modify url=https://mydomain.com/script.php
form request with=XMLHttpRequest
post data=location={USA|UK|Canada|Australia|New Zealand}&login=%login%&password=%password%
just download=1
Instead of SER spinning the locations and picking one at random (eg Canada), what gets posted is the whole spintax line ({USA|UK|Canada|Australia|New Zealand}). Is this a bug or has spintax been disabled here?