I may have made some observations elsewhere on this - but just in case you were not aware of this issue - bear in mind that the automatic insertion of field labels from the insert field dialogue and the newer field picker add un-asked for local styles to your layout.
You will be aware that best performance is obtained by having no local styles - i.e. all styles being incorporated in a theme - hence everytime you use the automatic insertion of field labels you are added a local style which is retrograding your performance. The label style is treated as the default text style and thus the default text style shows a change has been made - if you choose to update your style then the default text style becomes whichever right justified version style your labels carry - the field insertion and field picker actually add slightly different styles.
Once you know this happens it is easy to deal with - if a bit of a chore.
FMI are aware of this behaviour and I think regard it as a tidying up item to be dealt with at a later date.