First, observe when the switch happens

Note whether the input source changes after you click another document, move to another app, or press Control-Space, Globe/Fn, or Caps Lock. Also distinguish an actual macOS input source change from a Chinese/English mode change inside a third-party input method. Input Method Manager controls enabled macOS input sources, not an input method’s internal mode.

Four common causes

1. macOS remembers each document

Open System Settings → Keyboard and choose Edit next to Text Input. “Automatically switch to a document’s input source” may restore the source previously used in that document.

2. Keyboard shortcuts conflict

Check System Settings → Keyboard → Keyboard Shortcuts → Input Sources. Control-Space may also be claimed by an editor, remote desktop client, or another utility.

3. Caps Lock or Globe/Fn changes input

Chinese input source options can use Caps Lock to switch to ABC, while the Globe/Fn key can be assigned to change input sources. Keep only the behavior you intend to use.

4. Your workflow needs an explicit rule

If Terminal should always use ABC and chat should always use Chinese, per-app rules are more precise than document memory. If every app should stay on one source, use a lock.

Choose the behavior you actually want

  • Keep document switching when each document should remember its source.
  • Turn off unwanted automatic switching and lock one source when everything should stay the same.
  • Create per-app rules when different apps need different sources.
  • Change only the shortcut when accidental key presses are the problem.
Input Method Manager showing the current macOS input source and lock control
Input Method Manager can lock an input source that is already enabled in macOS.

Locking and automatic per-app switching are mutually exclusive, preventing two rules from competing. Automatic switching stops when the app quits.

Verify with three rounds of switching

  1. Move between two text fields in the current app.
  2. Switch between two apps three times.
  3. Use the shortcut you kept, then return to the original app and confirm the expected source returns.

If the result is still inconsistent, turn off both Input Method Manager automation modes and verify macOS alone before enabling one mode again.