Up, Down and Sideways

[Richmond]

I'm having the sort of fun I seem to have just about once a year:

mucking around with modifier keys . . . but, am trying to have even more 
fun than last year like this:

on mouseUp
--1
    if shiftKey() is up and altKey() is up then
       put "shUP-altUP" into fld "CRAP"
    end if
--2
    if shiftKey() is down and altKey() is up then
       put "shDN-altUP" into fld "CRAP"
    end if
--3
    if shiftKey() is up and altKey() is down then
       put "shUP-altDN" into fld "CRAP"
    end if
end mouseUp

and wondering, quite desperately in fact as quite as it rides on this,

why IF loop #3 doesn't work

if one exchanges '=' for 'is' it makes no difference.

the Documentation states that:

the altKey
altKey()

"Returns the state of the Alt key."

and that just doesn't seem to be happening [Linux].

Richmond.