Issue with unreliable controller input

For my FF6 T Edition translation patch, I want to include a text message that pops up when the player turns the system on. I first tried using some homebrew code to display a custom image, but that turned out to cause the Equip menu to freak out, so I've switched to a different approach.

My goal is to have this text message box pop up before the title screen:



I modified the standard event scripting to make this box + text appear before the title screen. It works fine now, except for one problem: the game often fails to recognize button presses when this box is displayed. Sometimes it won't recognize the A button, sometimes it won't recognize the B button, etc. But most of the time it just doesn't recognize any buttons at all, making it impossible for the player to progress through the text box.

I checked/watched/fiddled with various controller-related SNES registers, but with no clear change in behavior. I'm hoping that maybe someone here might know more about this sort of issue.

My event script code for this looks like:

Code:

$96 (fade in)
$4b,$00,$80 (display Bank 0, Line 0, at bottom of screen)
$b2,$29,$5e,$00 (jump to the pre-existing title screen event script at $ca5e29 as is normal for FF6T)
$fe (return)

I'm really stumped as to why the controller acts so unreliably. It works more reliably in bsnes than snes9x, but I get the feeling it's simply because of how they both initialize RAM.