Found it:
"Players can no longer initiate a trade with players casting a spell."
http://eu.finalfantasyxiv.com/lodest...f30908c0bd0c4d

This meant we could no longer be trolled while casting teleport. My guess is this was implemented in certain versions of FFXIV that was accidentally left out of the final code for the international Stormblood release.

Could we please have this back?