sheet references have been added on all references to the same sheet

Using LibreOffice spreadsheet on Ubuntu 16.
After a recent update, I find that all internal references within a sheet are prefixed with the sheet name: eg on ThisSheet where I had in C5: “=C3+C4” this have now been changed to “=$‘ThisSheet’.C3+$‘ThisSheet’.C4”. I did not ask for this change to happen…
This has made equations cumbersome due to the length of unnecessarily referring to the same sheet.
How can I globally remove these unnecessary references?

You seem to be using an old version, 5.1.x or such. Please upgrade. See this Why does Calc add unnecessary sheet reference? Can I prevent it from doing so? same question.