PubChem Data Sources

Data TypeLive Substances(444)Live BioAssays(81)Annotations(50)On Hold BioAssays(10)Classifications(7)On Hold Substances(5)

This is confusing. What are the onhold Substance and Bioassays? I will link to this from the article, http://nar.oxfordjournals.org/content/44/D1/D1202.long,
but it seems that data submission using pubchem upload, a data source may have some data on hold, and other data live.

Item URL: 
https://hypothes.is/a/G504wMLkEeafGh_HgqKgaQ