• VSCode Version:
  1.25.0-insider

• OS Version:
  Windows 10.0.16299.429

Steps to Reproduce:

1. Set window.titlebarStyle to 'custom' (and reload).
2. Open any document, and press 'Alt + Shift + F' (or any other keyboard shortcut that uses 'Alt' I presume - not tested).
3. The menu-bar's menu will show as well as activating the keyboard shortcut's action.

Maybe it has something to do with the editorTextFocus variable on the keyboard shortcut?

Does this issue occur when all extensions are disabled?:
Yes