Someone searched for the following statement the appropriate answer:
"My Papillon's ears fell down"
Yes, this situation does happen occasionally: a Papillon puppy can develop first regular erect ears, and then some months later drop those ears down to be a Phalene.
Remember, there was first the Phalene, the Papillon breed was mastered much later, but there are Phalene genes in all of them. Some litters get born from a Papillon sire and dam, but the pups are Phalenes, or vice verse.
If you want to make relatively sure to get a Papillon or a Phalene, you must look at the pups relatives several generations back. If they show a strong line of Papillons, you most likely have a Papillon puppy. If you see some Phalenes, and some Papillons in the grand parents, you can be surprised with either one.