Below i consider a two index keys where one (shorter) key is a full prefix of another (longer) key, for example:
- 'aa' and 'aaa'
- '' and 'a'

The rule :
- in ascending index short key is less then long key ('aa' < 'aaa', '' < 'a')
- in descending index short key is greater then long key ('aaa' < 'aa', 'a' < '').

The validation code is not detect the cases when rule above is violated.
For example, corruption at CORE-3839\CORE-3841 is not detected.