First, sorry my first comment wasn't super detailed or helpful. We're approaching a deadline, and it was super late for me, so I wrote it in kind of a panicked haze. I assumed the plugin was working as intended rather than being bugged somehow, but in hindsight I wouldn't be surprised if it's interacting poorly with another plugin.
I'm playtesting this one through someone else since I bought the plugin for him, so I'll have to wait for him to wake up to test it myself on a clean slate.
For more information, though (in case you wanted to quickly try replicating it), the issue isn't parallel events or a crash.
If we show a message normally without plugins, the game waits until hitting a confirmation key before running any code after it on the same Event page. (i.e. if we showed a message, then immediately set Self Switch A to true, Self Switch A would remain false until that message box was gone.)
If we ask the player to input text with this plugin, MV doesn't wait. All of the contents under it continue running. (i.e. If we call text input, then immediately set Self Switch A to true, Self Switch A will become true as we're still inputting text.)
Because of this, when a message is shown right under text input, MV seems to be getting confused on what to display where. The default input text is partially overwritten, and text disappears from the beginning of the box in a typewriter effect.
If it matters, the default input text is something like "(Type with your keyboard!)," parentheses included.
This happens consistently on MV, so if it's not a conflict with another plugin it shouldn't be hard to track down. Will update once I can test it myself with my teammate.