Animation Sometimes Shows Error dt >= 0

From time to time I get the following error while running in Unity editor player:

 Error dt >= 0 
 (Filename: /Applications/buildAgent/work/14194e8ce88cdf47/Runtime/Animation/Animation.cpp Line: 1983)

As stated in question What causes dt >= 0? it is an assertion and hitting continue let the game proceed as usual. I haven't found any hint about the source of this error as the game was running for months without problems. Then the problem reappeared recently after I had changed the AnimationState's speed property for some transition animations used in conjunction with CrossFade and PlayQueued.

I am sure that the fading time is still below 50% of the animation length (considering the increased speed already).

1. Is there any solution workaround?

2. How do I get more information about the source of the problem?

3. I haven't noticed this when deploying to iPhone - may I ignore it in the worst case?

I am using Unity Pro 3.5.6f4 and iPhone Pro.