A level 5 paladin gains the spell-like ability special mount that, in part, says that "the paladin may release a particular mount from service (if it has grown too old to join her crusade, for instance)" (Player's Handbook 44).
When such a mount is released from service, does the paladin first employ his spell-like ability to bring before her the mount then take a free action (as if to dismiss the mount) to release the mount on the Material Plane right there in front of her, the mount thereafter acting of its own accord? (As a spell-like ability of the calling subschool, the mount gains "the one-time ability to return to its plane of origin, although the spell[-like ability] may limit the circumstances under which this is possible" (173), but the creature doesn't have to use that one-time ability, like, right away or anything!)
Or is releasing such a mount from service a mental—or even spiritual—act that takes some indeterminate amount of time (metaphorically) off-screen so that the old, released mount remains in the celestial realm and a newer mount appears when the paladin next employs her spell-like ability special mount?
Or is releasing a mount from service done in some entirely different way?
Note: Ultimately, I'm uninterested in the special mount ability of the paladin per se and, instead, interested in the identical ability of the City of Splendors: Waterdeep prestige class knight of the Blue Moon (81–4) and like classes that lack the paladin's considerable baggage (so that other nongood monsters might be options). Don't get too hung up on the alignment or code implications of possible outcomes. Consider, instead, paladin as a placeholder for any class with the special mount spell-like ability.
See, I'm doing a bit of world-building and trying to figure out where monsters come from. I'm considering the spell-like ability special mount as one origin of the setting's monsters. That is, if a dismissed special mount can opt to remain on the Material Plane, a by-the-book campaign setting may be populated by any number of celestial heavy warhorses, giant eagles, giant owls, unicorns, and other creatures that were called as mounts then immediately released from service at the rate of one per day per each of the setting's high-level paladins et al. since the dawn of paladinhood (or since the dawn of the Knighthood of the Blue Moon or, y'know, whatever). (This DM can imagine a high-level paladin that's hopelessly stuck ruling a kingdom ("I must wear the crown for the greatest good, but it's so boring being queen!") using her otherwise pointless summon mount special ability for just such a purpose!)
