Short answer. In three situations under Article 1096 of the Civil Code: when the testator himself made the partition, absent a contrary intention and subject to the legitime remaining unimpaired; when the co-heirs expressly stipulated no warranty, absent bad faith; and when the eviction stems from a cause arising after the partition or the distributee's own fault.
What the law says
The obligation of warranty among co-heirs shall cease in the following cases: (1) When the testator himself has made the partition, unless it appears, or it may be reasonably presumed, that his intention was otherwise, but the legitime shall always remain unimpaired; (2) When it has been so expressly stipulated in the agreement of partition, unless there has been bad faith; (3) When the eviction is due to a cause subsequent to the partition, or has been caused by the fault of the distributee of the property.
Civil Code, Article 1096 — When Warranty Ceases. Read the full provision →
When the testator made the partition himself
Article 1096's first exception applies when the testator himself has made the partition. Ordinarily co-heirs must warrant each other's shares against eviction, but where the testator did the dividing personally, that mutual warranty obligation ceases, unless it appears, or it may be reasonably presumed, that his intention was otherwise. Even here, though, the article adds a firm limit: the legitime shall always remain unimpaired, meaning this exception cannot be used to defeat the minimum share the law guarantees to compulsory heirs.
When the co-heirs agreed to waive the warranty
The second exception applies when it has been so expressly stipulated in the agreement of partition. If the co-heirs themselves agreed, as part of dividing the estate, that no one would warrant the others' shares against eviction, that agreement is generally honored. This exception has its own limit as well: it does not apply unless there has been bad faith, meaning a co-heir who acted in bad faith cannot hide behind a waiver clause to escape responsibility for it.
When the eviction arises from a later cause or the distributee's fault
The third exception looks at the source of the eviction itself: it applies when the eviction is due to a cause subsequent to the partition, or has been caused by the fault of the distributee of the property. If whatever caused a co-heir to lose the property happened after the partition was already completed, or happened because that co-heir's own conduct brought it about, the other co-heirs are not held responsible for a loss unconnected to a defect existing at the time of division.
Why these exceptions exist
Together, these three situations recognize that the general warranty among co-heirs is not meant to cover every possible way a co-heir might later lose property, only losses connected to defects that existed, or should have been guarded against, at the time of partition. Where the testator controlled the division himself, where the co-heirs knowingly waived the protection in good faith, or where the loss came from something happening afterward or from the affected heir's own fault, imposing liability on the others would not serve the warranty's purpose.