Mathf.FloorToInt bahavior changed from 4.6 to 5.0.
In 5.0:
When the floating point value gets close to int.MaxValue or greater, the return value goes massively negative then tends towards zero.
In 4.6:
It just stays massively negative: -2147483648.

There's attached script "script.cs", which depending on Unity version (4.6 or 5.0) gives different value on 'more' public variable. Just drag it to any object in new scene and enter play mode to see it.