From Jeffrey Morlan:

pst_build_id_ptr and pst_build_desc_ptr require that the first child
of a BTree page have the same starting ID as itself. This is not
required by the spec, and is not true in many real-world PSTs
(presumably, the original first child of the page got
deleted). Because of this, many emails are not being extracted from
these PSTs. It also triggers an infinite loop in lspst (a separate
bug, also fixed)