I've created a spreadsheet with lots of buttons, each being assigned a
different macro.
However, every time I open the spreadsheet, these macro links disappear. So
I have to right click on every single button in the spreadsheet and assign
the macros again from scratch.

Why is this happening? And how do I make sure that the system remembers
which macros I've assigned to the various buttons, every time the spreadsheet
is opened?