Bicep cannot find EntraId group to configure as flexible PostgreSQL EntraId admin

[BasJanssenQuadira]

Bicep version
Bicep CLI version 0.39.26 (1e90b06e40)

Describe the bug
When trying to configure an existing EntraId group as administrators for an instance of Microsoft.DBforPostgreSQL/flexibleServers@2025-06-01-preview using the 'Microsoft.DBforPostgreSQL/flexibleServers/administrators@2025-06-01-preview resource results in an error message indicating that the group could not be found, as it would be duplicate.

I have tried to reference the group both by the Display Name and UniqueName properties, but neither results in Bicep selecting the existing group.
I have also tried using the Microsoft.Graph/groups@v1.0 as an existing resource that references the group using the UniqueName, which is successful, and referencing that resource in the administrators resource. This also results in the attempted creation of a new group that then conflicts.

I would expect Bicep to be able to reference the group correctly.

To Reproduce

resource postgresServer 'Microsoft.DBforPostgreSQL/flexibleServers@2025-06-01-preview' = {
  name: '${projectName}-prod'
  location: location

  tags: tags

  sku: {
    name: 'Standard_B1ms'
    tier: 'Burstable'
  }

  properties: {
    authConfig: {
      activeDirectoryAuth: 'Enabled'
      tenantId: tenantId
      passwordAuth: 'Disabled'
    }
    administratorLogin: <admin-user>
    administratorLoginPassword: adminPassword
    dataEncryption: {
      type: 'SystemManaged'
    }
    maintenanceWindow: {
      customWindow: 'Enabled'
      dayOfWeek: 6
      startHour: 5
      startMinute: 0
    }
    network: {
      publicNetworkAccess: 'Enabled'
    }
    replica: {
      role: 'Primary'
    }
    replicationRole: 'Primary'
    storage: {
      autoGrow: 'Enabled'
      iops: 240
      storageSizeGB: 64
      tier: 'P6'
    }
    version: '17'
  }
}

resource productionOwnersGroup 'Microsoft.Graph/groups@v1.0' existing = {
  uniqueName: <uniqueName>
}

resource dbAdmin 'Microsoft.DBforPostgreSQL/flexibleServers/administrators@2025-06-01-preview' = {
  parent: postgresServer
  name: guid(postgresServer.name, '/', <GUID>)
  properties: {
    principalType: 'Group'
    tenantId: tenantId
    principalName: productionOwnersGroup.uniqueName
  }
}