I've noticed a funny occurrence between files. In one of my assemblies I added holes using the Hole Wizard in assembly and those holes stayed in the assembly. When I did the same thing to a similar assembly the holes transferred to the part file as a derived feature.
First assembly with exlpoded feature tree (older):
Second assembly with exploded feature tree (newer):
As you can see in each picture the features are added in assembly but in the bottom picture (newer part) the feature has transferred into the part as a derived feature. These models were made a few months apart so I'm wondering if this is maybe a change made in a later service pack or if its something I've changed in my modelling technique without realising.
Using Solidworks 2014 sp5 for the newer part, probably sp2 for the older part but unsure.