Filemaker xsl-query does not return result

Hi!

I have a Filemaker server setup to handle xslt-queries, and mostly it works fine, but one case drives me nuts.

I have a table called Contacts with a field named OptionOne. The OptionOne-field is a calculation with the result (0 or 1) calculated from data in another other table. The result displays nicely in filemaker:

Name OptionOne

Aaaaa 1
Bbbbb 0
Ccccc 1
Ddddd 0
Eeeee 0

However, when I run the query with xslt, I get the correct result only when I query for OptionOne=0

 http://myfilemakeraddress?-db=Contacts&-lay=web&OptionOne=0&-find

Bbbbb 0
Ddddd 0
Eeeee 0

The similar query for OptionOne=1 does not return anything!

http://myfilemakeraddress?-db=Contacts&-lay=web&OptionOne=1&-find

What is it with this search for "1"? And is there a way to search for all empty records? All not empty records?

The underlying Filemaker expression for this field is: If(not IsEmpty(AnotherTableField1) or not IsEmpty(AnotherTableField2);1;0)

Regards!