how can users be removed from contributor list?

[Valient Gough]

When a translation template is displayed, it shows a list of 
"Contributors for this translation".  What can cause a user to be 
removed from this list?

I ask because I have been using a script to periodically downloading all 
PO files, and contributor lists for my project.  I had expected that the 
contributors list would only increase in size, but a diff between today 
and the two days ago shows that 2 new contributors were added, but one 
was deleted.  I no longer see any sign of him in the contributor lists 
when I look online..

regards,
Valient