This if statement will not return a result:

"ID" = 1

"BD" = 2

"FK" = if("ID">"BD",sqr(("ID"/"BD")^2 - 1),0)

I am guessing that it is because both expressions in the if statement are evaluated, the sqr function fails and therefore the whole expression fails.  I think this bug was also present in SW 2010.  These are the sorts of things that caused me to let my subscription lapse for four years.