One possibility that is particularly problematic is when the new species is discussed in another publication that happens to get published first.  This may happen when a general study collects new taxa that are sent to someone for study.  If the general publication comes out first, often the new species gets mentioned.  If the description is sufficiently detailed, this constitutes the actual publication.  Thus, if Jones publishes "Xus yus, a new species being described by Smith, is common at the new locality.  It is distinguished by ..., as seen in figure 1" before Smith publishes his description, the species could become Xus yus Smith in Jones.  If Jones publishes "Xus yus, a new species, is common..." and does not specifically mention Smith at that point, the species could even end up officially Xus yus Jones, even though Jones did not mean to cut Smith out of it.  Use of unpublished names is always a risk.

Dr. David Campbell
    "Old Seashells"

    NEW ADDRESS AS OF 8/21/00
    Biology Department
    Saint Mary's College of Maryland
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    "He had discovered an unknown bivalve, forming a new genus"-E. A. Poe, The Gold Bug