I do not really agree with the comments that tend to underestimate the importance of coding styles.
I think that good and widely known good coding rules are important for an engineers (I do not design product, I teach HDL languages).
Good software design and coding rules is exactly what leads to modern high performance software.
In this particulkar example, it happens that the 'full case statement' is something that many HDL designers do not suggest to use.
If Quartus requires this kind of coding, this is something that will bring me to use other synthesizers (and good coding styles) when I need to obtain high performance circuits.
I hope that Altera is able either to explain this behaviour or modify it.