With manticores, gorgons and ankhegs it's pretty clear the RA are, or were, experimenting with chimera variations, getting clapped by one of your escaped experiments is pretty thematic.
RA members would be expected to use invisibility when travelling (cast or brewed in the case of warmages / illusion restrictions), but aside from that, the manticores already spawn away from the transition. If you found them impassable without being spiked, they either wandered from the area being loaded for too long, or someone lured them, moving them slightly more would be redundant in the latter case. The domain isn't meant to be safe, anyway.
It's the Forbidden Forest to your Hogwarts.