The keyboard shortcut for editing a page through the VisualEditor is Alt+⇧ Shift+V. The same key combination happens to be used for the Show changes button in WikiEditor. Therefore, while in source editing mode, pressing this shortcut causes the switch to Visual editing instead of showing changes in Source editing.
This couldn't have been by design, could it?
I can't reproduce this on my Mac in Safari (the equivalent keyboard shortcut does nothing). Can you tell me your web browser and computer operating system? Also, does it matter whether the cursor is inside the editing box (rather than outside of it, e.g., in the search box)?
Windows10 1903, Chrome v79.0.3945.130 (64-bit). Placement of cursor makes no difference, checked at all locations (header, footer, sidebar, preview area etc.).
On Firefox v72.0.1 - there, the keyboard shortcut toggles focus between the two Show changes and Visual editing buttons, probably the same as Safari.
On Microsoft Edge - Usually the Visual editing button is given preference, unless the cursor is specifically on the two: "Pages transcluded onto the current version..." and "This page is a member of ... hidden category..." lines, then the Show changes button is activated.
On Chromium-based Edge beta v80.0.361.33 - the same thing happens as in Chrome.
