Is tile spawning under fast movement bugged?

I am aware of 2048's spawning rules:
spawn 2 in random empty spot 90% of the time
spawn 4 in random empty spot 10% of the time

I have noticed it's possible to avoid such a situation by pressing up and then down in quick succession causing both tiles to spawn above the rest. Is this intended behavior?

As this question is implementation specific, I'm playing this version in my computer and this version on my iPhone. This occurs in both versions.

Clarification (underscore "_" denotes an empty tile):

What I expect:

2 4 2 _  
4 2 _ _  
8 _ _ _  
2 _ _ _  

Press right (4 spawned)

_ 2 4 2  
_ _ 4 2  
_ _ _ 8  
4 _ _ 2  

Press left (2 spawned)

2 4 2 _  
4 2 _ _  
8 _ _ 2  
4 2 _ _  

What I observed if keys are pressed fast enough:

2 4 2 _  
4 2 _ _  
8 _ _ _  
2 _ _ _  

Press right (nothing spawns)

_ 2 4 2  
_ _ 4 2  
_ _ _ 8  
_ _ _ 2  

Press left fast enough (two tiles spawn)

2 4 2 _  
4 2 _ _  
8 _ _ 4  
2 _ _ 2