That's definitely a strange situation you've got there. The problem has something to do with the quantifier in the regex. When I replace /^([A-Z]+)$/ with /^([A-Z]*)$/ (i.e. change the '+' to a '*') I get...

In if:   FOO
In else: 
In else: 
In if:   BAR
In else:
[download]

while changing the regex to /^([A-Z]{2,})$/ results in...

In if:   FOO
In else: FOO
In else: 
In if:   BAR
In else: BA
[download]

While experimenting with {0,} {1,} {3,}, etc. it seems like in the non-matching case, $1 contains characters from the previous match and the number of them depends on the value for the minimum quantifier of the regex . I wouldn't try to depend on this behaviour if I were you:-)