Option-Arrow on a command prompt prevents text from being edited/deleted

Hello!

I'm running the latest version and I'm not sure what is going on. I tend to have a pattern where I'll up-arrow through my history to find a command, and then need to modify it slightly. So let's say I have the following command:

cp ~/mydirectory/home ~/mydirectory/home_backup

And I've forgotten the -r. So my workflow is I'll hit up-arrow to bring the command up again, and then I use option-left-arrow to move by word to just before the cp command. But when I type it doesn't always insert characters, and I find that also once I type I can't seem to delete before where I started typing. So using the above example, if I option-left-arrow to the first tilde, and then try to type, I can't ever delete (or even get to!) anything earlier in the line than that.

I'm sure this is a behavior I don't understand, but is there any way to turn that off? Or to help me understand what it's doing? (It doesn't seem to be a Vim mode, but maybe it's an Emacs mode and I don't use that?)

Thanks!

Reproduce the reported command-prompt behavior by recalling a command with up-arrow, moving with Option-Left-Arrow, and trying to insert and delete text. Inspect the repository's zsh and command-prompt configuration to identify the behavior, then confirm that the relevant setting is explained or corrected.