if() function behavior

I have a statement in my form like this:

<xforms:setvalue xforms:ref="instance('instance00')/brands/brand3" 
value="if(string-length('203') &gt; 4,substring('203',5,1),'')"/>
When executed, I get "java.lang.StringIndexOutOfBoundsException: String 
index out of range: -1".
It looks like the "substring('203',5,1)" part is evaluated even if the 
"string-length('203') &gt; 4" part returns "false". Is this normal 
behavior?
I am trying to split a value submitted from a SELECT control - like 
'204060708' - into values "2", "4", "6"... that I can insert into 
individual nodes of the instance tree.
A.



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