Since Unity 2021.2 the inspector got ability to evaluate better math expressions. For example, entering "+=3" adds 3 to the current value.

The issue is that the expression is re-evaluated based on current value for every new character typed into the field. You'd expect typing "+=333" to increase the value by 333, but instead it increases by 369 (+=3, +=33, +=333) unless you paste the full expression in one go.

Steps:
1. Create any object at 0,0,0 position.
2. Type (not paste!) "+=333" into say position x field.

Results: position is 369 (i.e. 3+33+333).
Expected: position is 333.

A proper way would be to store the initial values, and evaluate expressions against the value when the user stared to edit the field, instead of current value.