OWL-2 property chain with a data property

Hi all,

I haven't clear the issue in the subject. I have this situation:

class *fibo_bft:Percentage* 
(http://www.omg.org/spec/EDMC-FIBO/FND/Utilities/BusinessFacingTypes.rdf)
   having the data property *fibo_bft:hasPercentageValue*

I'd like to simplify it in my own ontology:

new object property: *my:has-percentage*, range: fibo_bft:Percentage
new datatype property: *my:has-percentage-value*
   as equivalent to: my:has-percentage o fibo_bft:hasPercentageValue

I've tried to define the axiom above in Protegé 5.2:
- I cannot define a datatype property as subproperty of a chain axiom
- but I can do it for object properties

So, I defined the the above manually, by editing the ontology .owl file:
>     <owl:DatatypeProperty 
> rdf:about="http://www.example.com/terms#has-percentage-value">
>         <owl:propertyChainAxiom rdf:parseType="Collection">
>             <rdf:Description 
> rdf:about="http://www.example.com/terms#has-percentage"/>
>             <rdf:Description 
> rdf:about="http://www.omg.org/spec/EDMC-FIBO/FND/Utilities/BusinessFacingTypes/hasPercentageValue"/>
>         </owl:propertyChainAxiom>
>     </owl:DatatypeProperty>

  but, when I reload it in Protegé, my:has-percentage-value is both a 
data property and an object property.

Question: is *owl:propertyChainAxiom* available for object property 
only, or is this a bug in Protegé?

Thanks in advance,
Marco