Message List View: Typing ESC in search-bar has consistently inconsistent behavior

Current and desired behavior:

1. Click on the search bar in the upper right of the message view.
   
2. Type a few characters as if searching for that string.
   
3. Instead of return, press Escape
   
4. Results:
   
   • Search bar is cleared and focus goes back to the message list

Current and undesired behavior:

1. Click on the search bar in the upper right of the message view.
   
2. With no characters entered into the search bar, Immediately press Escape
   
3. Expected and desired Results:
   
   • Search bar is cleared and focus goes back to the message list
4. Observed Results:
   
   • No-op

This seems inconsistent. It may be my keyboard mappings (I've done extensive customization but don't believe that I've fiddled with the Escape key).