Highlight problem when reusing variables

[yfaria]

The WQL query

_chase_v_1[arg2 z] 
_dog_n_1[arg0 z]

In particular, this query has an interpretation: we are basically searching for sentences where a dog is being chased.
Even though the SPARQL resulting from it makes sense and we get the right results, there is a highlighting problem.
.
In this case, it's easy to see that the match happened associating WQL's z variable with the MRS x3 variable, and the corresponding MRS variable is highlighted but only in the predication with _dog_n_1.

Actually, if we look at the SPARQL resulting query, we have

The problem is that we are selecting the SPARQL variable ?x5 two times and the second occurence was ignored on the output.

I should investigate whether this problem only occur with AllegroGraph or it's about SPARQL specification and how to solve it.