hash concatenation messes key ordering

Hello

This FreeMarker template:
<#local foo={'a':'1','b':'2'} />
<#local foo=foo+{'c':'3'} />
<#list foo?keys as k>
${k}
</#list>

prints:
b c a

Would it be possible to concatenate 2 hashes in FreeMarker but retain 
the key ordering? (so it would print "a b c")

What I'm asking already happens in sequence concatenation, so:
<#local foo=['a','b'] />
<#local foo=foo+['c'] />
<#list foo as k>
${k}
</#list>

prints:
a b c

I'm using FreeMarker ver 2.3.15


thanks a lot!
Ioannis


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