It seems that the maximum number of labels is limited by the parameter "Maximum number of hashtags per article" = ex 5.
I do not know if it's voluntary. But this is a little strange for the user in practice, he has a list of 15 labels, he chooses 10 but only 5 are saved. I understand that these are predefined hashtags, but in the case of labels, should not this be independent?
Thanks Alex, yes, in my case, I found him a more particular use, allows to choose among a list of topics of discussion topic, and thus find people with common points in one click. Very interesting for me.