Description of problem:

Looks like that current locking mechanism relies on preventing selection of a locked activity instead of disabling panels. Basically when I manage to select an activity which has been locked I can change what ever I like.

Locked Activity Modification 1
1) Select an activity
2) Lock it (properties panel has not changed because the activity remains selected so it is still modify the activity)
3) Attempt to modify something

Locked Activity Modification 2
1) Select an locked and deselected activity using the many selection
   a) click and hold the left mouse button
   b) select only the locked activity
2) Attempt to modify something