Cannot validate a contained resource with Simplifier.net - hl7-fhir

Question

We are testing against SIMPLIFIER.NET the FHIR resource shown below.
It is an Encounter containing a Task. As encounters cannot reference tasks directly, we are using reverse references.
According to the standard R4, "For a resource that references the container, the reference is '#'."
Problem is that Simplifier throws exceptions in that case, while Confluence and Gazelle don't:
The question is: Is that FHIR resource well formed?
{
"resourceType": "Encounter",
"status": "planned",
"contained": [{
"resourceType": "Task",
"status": "requested",
"intent": "order",
"note": [{
"text": "Task 2"
}],
"id": "task1",
"encounter": { "reference": "#" }
}],
"class": {
"display": "Pre Op"
},
"subject": {
"reference": "Patient/83479"
},
"episodeOfCare": [{
"reference": "EpisodeOfCare/FC93408C-6E0E-4003-B984-A6B4CE7334B8"
}],
"basedOn": [{
"reference": "ServiceRequest/332276C4-12FA-4576-AE1D-6865C267BDD5"
}],
"participant": [{
"individual": {
"reference": "Practitioner/cea0b20a-e162-4065-a16d-766697e647ac"
}
}],
"meta": {
"lastUpdated": "2021-10-06T10:09:40.070-05:00"
},
"id": "B3E42476-A8FE-4848-9F2B-F3F9126E88C6"
}

Answer 1

The FHIRPath definition of the ref-1 invariant currently does not allow for referencing the container resource from the contained resource, only for referencing other contained resources:
reference.startsWith('#').not() or (reference.substring(1).trace('url') in %rootResource.contained.id.trace('ids'))
A ticket for changing this in the FHIR specification has already been filed and approved for changing this, but it has not yet been applied.