I create a clip using Face Key with discrete keyframes for expressions at various points in time.
If I then use Face Puppet to add ("blend" mode), say, eye movement to the animation, the keyframes previously created by Face Key disappear in the timeline (clip).
In fact, the Face Key-generated clip is replaced by a new "PuppetClip" in the timeline, where the Face-Key clip has somehow been merged into the puppet clip. 

This "destructive" operation makes it impossible to go back and adjust the Face Key keyframes.

Expressions REALLY need "layers" (like "Motion" has) for keeping things separated to allow animations to be created incrementally across multiple passes. That would include the ability to go back and adjust keyframes. Seems like I'm constantly fighting (or confused by) the timeline because of the way the system is always wanting to "flatten" things into one layer.

(As an aside, if you perform the above scenario with Puppet in "replace" mode instead of "blend", the program crashes).

iclone 8.23.