In Graduated Color or Graduated Symbol symbology, ArcMap allows you to set the Label to read whatever you want, rather than exactly what is shown in the Values column.
The problem is that the slightest change to ANY value in the Range column completely obliterates all of the other labels, potentially wasting a huge amount of time.
Eg, if I change the first Range value to be 250001 this is the result:
The logic should be that the Label is set to the Range when the Classification is first set (including on layer creation) but thereafter, any changes to the Label field are made by the user only, not automatically.