CHOOSE(0) constant-folded incorrectly

For the following code...

toText(UNSIGNED1 i) := CHOOSE(i,'one','two','elsevalue');
OUTPUT(toText(0));
OUTPUT(toText(1));
OUTPUT(toText(2));
OUTPUT(toText(3));
OUTPUT(toText(4));

The values 1 and 2 yield their counterparts, and the values 3 and 4 yield 'elsevalue' as expected. However, passing 0 yields 0.

Shouldn't passing 0 yield 'elsevalue'?

I do see I'm violating the expected type of input, as the first parameter is described in the user's guide as "An arithmetic expression that results in a positive integer and determines which value parameter to return". However, given the elsevalue is broadly described as "The value to return when the expression returns an out-of-range value", it seems more logical to return it rather than lapse into undefined behavior.