We recently installed SP 4.0 from SP 2.0 in 2014. What I've been noticing now (which seems to be new) is that Replace face sometimes works and other times doesn't but doesn't show in the tree that it has failed. Everything appears to be ok in the tree but looking at the actual geometry reveals that the Replace Face is no longer replacing the intended face.
It's not as big of a deal when creating a Replace Face for the first time because you can see right away it didn't work. The bigger problem is when it works and you continue in your design then later it decides it's not going to work anymore but not give any indication that it has failed. If you're not paying close attention to the actual geometry on the screen and know exactly what it's suppose to look like you will miss it all together.
In my case send out for prototype models only to realize the geometry is bad because a replace face has failed.