weird macro params issue

Hello

I have this macro:
<#macro test a b=a c=b>
    ${a} - ${b} - ${c}
</#macro>

And this client code:
<@test 1 /><br/>
<@test 1 2 /><br/>
<@test 1 2 3 /><br/>

Which produces:
1 - 1 - 1
1 - 2 - 2
1 - 2 - 3

Now if I just change the param names of the macro:
<#macro test foo bar=foo baz=bar>
    ${foo} - ${bar} - ${baz}
</#macro>

And keep the same client code, then the output produced is:
InvalidReferenceException: Expression bar is undefined on line 20, 
column 31 in index.ftl.
1 - 2 - 2
1 - 2 - 3

The first call fails when it tries to evaluate the baz=bar. Why is that?

Also, is this usage valid in freemarker? To have parameters default to 
the value of other parameters. I find it very useful for some use cases.

thanks,
Ioannis

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