The issue with the acf/load_field filter affecting the saving a fields when editing has always existed. When I say acf/prepare_field is newer, it was introduced in version 5.0.0, for most people they have probably never worked with ACF without this. Before this version I always added checks to my acf/load_field filters to check if an ACF field group was being edited before applying the field.
There should be more information given in the docs for these filters. acf/load_field more or less permanently alters the field unless you never edit a field group where acf/prepare_field is a temporary change applied just before the field is show.
