Graph.validate() results seem non-deterministic

[Maghnie]

Using the "bad building" example model from the tests directory (tests/data/badBuilding.ttl), we're not getting consistent validation results between different runs:

Output 1

Validation results of data\bad_building.ttl 
Validation Report
Conforms: False
Results (2):
Constraint Violation in OrConstraintComponent (http://www.w3.org/ns/shacl#OrConstraintComponent):
	Severity: sh:Violation
	Source Shape: [ sh:message Literal("A piece of Equipment can feed a Equipment or Location.") ; sh:or ( [ sh:class brick:Equipment ] [ sh:class brick:Location ] ) ; sh:path brick:feeds ]
	Focus Node: bldg:AHU1A
	Value Node: bldg:VAV2_3
	Result Path: brick:feeds
	Message: A piece of Equipment can feed a Equipment or Location.
Constraint Violation in ClassConstraintComponent (http://www.w3.org/ns/shacl#ClassConstraintComponent):
	Severity: sh:Violation
	Source Shape: bsh:hasPointShape
	Focus Node: bldg:VAV2-4.DPR
	Value Node: bldg:Room-410
	Result Path: brick:hasPoint
	Message: Value does not have class brick:Point
Graph is not valid!

Output 2

Validation results of data\bad_building.ttl 
Validation Report
Conforms: False
Results (2):
Constraint Violation in ClassConstraintComponent (http://www.w3.org/ns/shacl#ClassConstraintComponent):
	Severity: sh:Violation
	Source Shape: bsh:hasLocationShape
	Focus Node: bldg:Room-412
	Value Node: bldg:VAV2-3
	Result Path: brick:hasLocation
	Message: Value does not have class brick:Location
Constraint Violation in ClassConstraintComponent (http://www.w3.org/ns/shacl#ClassConstraintComponent):
	Severity: sh:Violation
	Source Shape: bsh:hasLocationShape
	Focus Node: bldg:Room-412
	Value Node: bldg:AHU1A
	Result Path: brick:hasLocation
	Message: Value does not have class brick:Location
Graph is not valid!

Any hint on what could be going on?