Keep in mind only local scale can be edited, due to how the math must work for scale. Parent and world scale cannot be edited. Because of that, when the scale text fields are focused the local scale is shown. The Local axes button is highlighted as a reminder.
Likely you have Parent or World axes selected, so when the scale text field loses focus, the value changes from local to parent or world. The scale value is applied as soon as you type it though, it is not lost when you press tab.
