Does multi-conditional if() function work differently between ER and Interface ?

Hi,

I found in an existant ER code this kind of multiple condition:

if(cons!TEST = "1",
  "VALUE 1",
  cons!TEST = "2",
  "VALUE 2",
  cons!TEST = "3",
  "VALUE 3",
  cons!TEST = "4",
  "VALUE 4", 
  cons!TEST = "5",
  "VALUE 5",
  ""
)

That seems to works fine, but when I put this condition in an interface and click on "DESIGN MODE", I obtain this error:

   "Cannot load Design Mode : The function ’’if’’ [line 275] has 3 parameter(s), but instead passed 11 parameter(s)."

Where is the truth ?