I've learned this today, having watched a bit of FF4's PSP version...
Apparently, there is code there to react to summons for Rubicante. When hit by a summon, Rubicante proceeds to cast Ice2/Blizzara on himself. This doesn't seem to change whether or not the "cloak" status is active.
This code doesn't appear in FF2US or FF4ET. I don't quite understand why... (it's very similar to Scrmaglione's missing Slow counter vs Fire magic).