Multiple level filtering not behaving as expected and not consistant behaviour between ${} replacement and @@ replacement

A filter can be made up of multiple parts such as myproperty1 and myproperty2 below:

part1=part1
part2=part2
myproperty1=${part1}-${part2}
myproperty2=@part1@-@part2@

It is possible to define a second filter file (which should take precedence over the first filter file) to override some properties from the first filter file.

When the second filter file overrides part1 (for example) my expectation is that both ${part1} and @part1@ will be taken from the second filter file when replacing myproperty1 and myproperty2 in any filtered resources. I would expect the result of filtering myproperty1 and myproperty2 to be the same.
However in reality myproperty1 and myproperty2 produce different results.

There is no documented precedence of delimiters - I expect ${} and @@ to behave the same.

Also my expectation is that ${part1} will always be taken from the second property file when it is overwritten there.

I have attached a project which demonstrates the issue.