BiT with Epona

I was doing a 100% run on GC, just got the heart piece from Ordon Ranch. Saved while on Epona, got off Epona, LJ'ed the loading zone trigger, and did a shield bash buffered BiT. When the title screen loaded in BiT, I was on Epona.

I may have been a bit quick in my initial A press, because I didn't get off Epona when I did so. I rode around for a bit before riding back in-bounds and getting Epona stuck up on the ledge near the lava storage area where there's a heart piece at the bottom. After that happened, I rode Epona around a bit up there before stopping, and hit A again. I noticed as the file selection screen was coming up that I was getting off Epona here.

Any ideas as to what causes this?

EDIT: Just in case it ends up being relevant:

1.0 NTSC GC
Normal 100% route from ~2 months ago (not Fixed EMS route)
After pausing to explore it a bit, I loaded another file I'd made in the run right by the Ordon Bridge (used initially for gameplay after the initial BiTE for Early Monkeys), BiT off that and I was as normal on the ground, not on Epona. Resumed the run from there.