2 answers
Beacause you have multiple fields in your CASE statement.
CASE functions work like this:
CASE(TheField,
"The Field Value 1", Result 1,
"The Field Value 2", Result 2,
"The Field Value 3", Result 3,
NULL)
your formula is doing something like:
CASE(TheField,
"The Field Value 1", Result 1,
"The Field Value 2", Do another formula ,
"The Field Value 3", Do another formula ,
NULL)
