listindexer duplicating

Hello, I’m am taking over development/administration of a website that was built in modx. I am new to modx and have some questions in regard to a bug that I see:

There is some listindexer code: that is generating a list of weblinks to pdfs for each year. Below the 771 document there are containers for the years 2007, 2008, and 2009 which hold weblinks to each of these pdfs. Everything appears to be working great, except that the 2009 is duplicating its link when outputting (so there are two of each pdf links for 2009).

My questions:

1. Any idea how to go about troubleshooting this, or what could be causing this?
2. What does each of the parameters for the listindexer code mean?

Thanks in advance!

ok, I have figured out that if the document belongs to two document groups, it will duplicate it. However now I’m having the issue that when I try and uncheck one of the groups and save, when I re-open the document, the group that I unchecked remains checked..... any ideas on that?