I understood. I can’t duplicate it though.
Things that might affect the output:
Ensure each of the authors is on a separate line when you type them into the record.
Does it happen even if only one or the other of your examples are in a new document, by themselves. (affected by discussion below).
Is this happening at the first citation, or in a subsequent citation of the exact same author, title, year information? (affected by discussion below)
In my “out of the box APA 6th”, the first citation should show all authors if 6 or less, but in subsequent citations to the same reference, only show all authors if 3 or less. In each case, it will show just the first author, et al, if the number of authors is higher than 6 or than 3. This could affect what you are seeing, especially if the two refs you are testing are the exact same thing.
So if I insert the same refs in a document, twice, I get the following:
(Myllykangas, Buenrostro, Natsoulis, Bell, & Ji, 2011; Soderberg_, et al._, 2000; Zhou, Li, Yuan, & Kirschner, 1998)
(Myllykangas_, et al., 2011; Soderberg, et al., 2000; Zhou, et al._, 1998)
Myllykangas, S., Buenrostro, J. D., Natsoulis, G., Bell, J. M., & Ji, H. P. (2011). Efficient targeted resequencing of human germline and cancer genomes by oligonucleotide-selective sequencing. [10.1038/nbt.1996]. Nat Biotech, advance online publication. doi: http://www.nature.com/nbt/journal/vaop/ncurrent/abs/nbt.1996.html#supplementary-information
Soderberg, C., Wraith, A., Ringvall, M., Yan, Y. L., Postlethwait, J. H., Brodin, L., et al. (2000). Zebrafish genes for neuropeptide Y and peptide YY reveal origin by chromosome duplication from an ancestral gene linked to the homeobox cluster. J Neurochem, 75(3), 908-918.
Zhou, B. B., Li, H., Yuan, J., & Kirschner, M. W. (1998). Caspase-dependent activation of cyclin-dependent kinases during Fas- induced apoptosis in Jurkat cells. Proc Natl Acad Sci U S A, 95, 6785-6790.
And the way these records are entered are
(5 authors so show all 1st time, but only first author in second listing)
Jason D. Buenrostro
John M. Bell
Hanlee P. Ji
(7 authors, so just 1st author et al for both citations)
Yan, Y. L.
Postlethwait, J. H.
(4 authors, soshow all 1st time, but only first author in second listing)
Zhou, B. B.
Kirschner, M. W.
If you would like me to look at the refs in the library, please contact me thru the private messages.
Or insert the refs in a word document and save it. then in windows change the extension to one of the allowed extensions (like .ens) and tell us if the ext was .doc or .docx). This will let you attach the file even though it isn’t one of the accepted extensions…