For reference, the SRD entry for a bag of holding says this:
If a bag of holding is placed within a portable hole a rift to the Astral Plane is torn in the space: Bag and hole alike are sucked into the void and forever lost. If a portable hole is placed within a bag of holding, it opens a gate to the Astral Plane: The hole, the bag, and any creatures within a 10-foot radius are drawn there, destroying the portable hole and bag of holding in the process. Rope trick
, on the other hand, has one sentence on the subject that is much more general:
Note: It is hazardous to create an extradimensional space within an existing extradimensional space or to take an extradimensional space into an existing one.
What items mention 'bag of holding' or 'portable hole' as what they act like? Other than the two belts with the pockets that are miniature bags of holding?
Only ones that I know of are the ones you mentioned (belt of many pockets and it's nerfed version in the MIC) and Heward's Handy Haversack, which has two side pockets which are "like a bag of holding".