Tag FFEX

[orly-sharon]

HI,
I'm trying to generate tag FF Ex ( X=1, 2,3.... like -FFE1 /FFE2/FFE3),
when I sent to the builder this tag, the Ex is recognized as constructed tag. and builds it in the wrong way.
Ex ( X=1, 2,3....) is known as a constructed tag? why does the builder recognize it as one?

p.s
the tag FF 12 does not generate this problem