Strange behaviour of struts conditions

I can't succeed in making the conditions work as expected in struts.

Here is some sample code in my jsp :

1 - <s:property value="jobdef.interruptable"/><br/>
2 - <s:property value="jobdef.testable"/><br/>
3 - <s:property value="false && true"/><br/>
4 - <s:property value="false || true"/><br/>
5 - <s:property value="false && jobdef.interruptable"/><br/>
6 - <s:property value="jobdef.testable && true"/><br/>
7 - <s:property value="jobdef.testable && jobdef.interruptable"/><br/>
8 - <s:property value="false || jobdef.interruptable"/><br/>
9 - <s:property value="jobdef.testable || true"/><br/>
10 - <s:property value="jobdef.testable || jobdef.interruptable"/><br/>

which should print

1 - true
2 - false
3 - false
4 - true
5 - false
6 - false
7 - false
8 - true
9 - true
10 - true

but actually print

1 - true
2 - false
3 - false
4 - true
5 - false
6 - true
7 - true
8 - true
9 - false
10 - false

And these conditions are also wrongly evaluated in the struts if tag.

FYI, interruptible and testable are private Boolean fields with their public accessors in the JobDefinition class, and jobdef is an instance of this class.

Does someone know why it doesn't work as expected ? And how can I make the conditions jobdef.testable && jobdef.interruptable and jobdef.testable || jobdef.interruptable be evaluated rightly ?