Depends on the color, and of course, number one - Depends on who you got them from.
In Buffs it is very common due to a lack of people working on them, and in general a lack of common population.
In Silvers I've never heard of it.
In Brown-Reds I've never heard of it.
In Wheatens and Blue Wheatens I have heard of it, but thankfully not too often. There are some breeders out there who gaurantee having no issues.
In Blue, Black, and Splash it sadly does pop up. There are a few known breeders who it is far more common in than others, so watch out.
In Lavenders I've heard of it, but I think people are doing a pretty good job of trying to keep it on the low.
In Whites I've never heard of it.
Of course, many people don't care about it, but honestly it is a breed trait, a very well known one, that shouldn't be missing.