Constancy of gain bandwidth product for amplifiers
The GBW product of an op-amp is set by internal resistances or current sources, and an internal capacitor.  These are all made on silicon, and will be quite variable.  The one datasheet that I checked lists the GBW product as &quot;typical&quot;, without even giving a minimum and maximum.
Bottom line: if you're depending on the GBW product to be constant, you probably want to revisit the decisions you made designing that circuit.