Excel formulas starting to include current sheet name

Hi 

I recently noticed that formulas in excel starting to automatically include the "current" sheet name after leaving and coming back to the sheet (example below). I don't remember this used to be the case but I could be wrong. Does anyone have a similar experience or can confirm if this is correct?

Is there a setting somewhere I can turn this on and off?

Example: I have 2 tables (1 per sheet). After clicking on Sheet2 to select the cell I want to sum, coming back to Sheet1 and referencing any cells will include "Sheet1!" in my formula. I believe previously the formula omits "Sheet1!".

Both ways are useful in different scenarios but wondering if I have missed a trick to "turn on and off" how it behaves.

Thanks!