When you link to a cell that has a number format you may be surprised to learn that as well as the value that is linked, the format also is updated based on the cell you linked to.
Have a look at the image below where cell A1 has the currency format applied.
If I enter a value in cell C1 you see that it just displays the number with no formatting.
If I use a formula in cell C1 that links to cell A1, then the format (as well as the value) comes across from cell A1.
This only applies to number formats.