To reproduce:
1. Open project
2. Select 'cube' gameObject
3. Press 'PLAY' on 'Clip Player' script component
Notice, that animation is played.
4. Press 'NEXT'
Notice that 2nd animation clip is not played(if you press 'NEXT' again, 1st clip will be played properly)
5. Repeat 2-4 step while in play mode

Expected: both animations will be played in both Editor and Play modes
Actual: both animations are played only in Play mode (gifs attached)

Reproduced on: 2017.1.1f1, 2017.1.2p1, 2017.2.0p1, 2017.3.0b6, 2018.1.0a2