A number of erroneous attempts involving
PQ-trees in the context of automatic graph drawing algorithms have been presented in the literature in recent years. In order to prevent future research from constructing algorithms with similar errors we point out some of the major mistakes.
In particular, we examine erroneous usage of the PQ-tree data structure in algorithms for computing maximal planar subgraphs and an algorithm for testing leveled planarity of leveled directed acyclic graphs with several sources and sinks.
Partially supported by DFG-Grant Ju204/7-2, Forschungsschwerpunkt 
Effiziente Algorithmen für diskrete Probleme und ihre Anwendungen
and ESPRIT Long Term Research Project Nr. 20244 (ALCOM-IT)