CSSWG has resolved  to change the ordering of scroll-snap-align property to be in "block inline" order. WebKit parsing logic appear to do "inline, block" order.
I have changed Chromium implementation to match the specification but it is now different from Safari.
The current usage of two value is low but as it grows the interop issue problem grows.
- My backward compat analysis suggested the risk is low 
- Relevant WPT test .
I tested this on Safari 12.0.1.