Can someone explain how the filter works for the Select Work Items dialog when associating a work item to a change set?

When you use the Related Artifacts -> Associate Work Item... menu choice for an outgoing change set, you are presented with a "Select Work Items" dialog.  The dialog lets you filter by id or text.  I am having a hard time understanding how the filter by text works.  I have tried using it for a long time now and always seemed to get random results when searching by text.  Searching by id works fine.  I will put in some text that I know should match a particular work item and it won't show up in the result.  I had given up on using it for anything other than id matches.  Recently, I had some co-workers who said they had been using it to find work items assigned to themselves or other by entering their last name in the search.  Then, earlier this week, that stopped working for them.  There has been no changes to the server or the process configuration made since it had been working for them to when it stopped.  I had said I have never seen it do anything that made sense. 

So, that is what has lead me to post this question.   What rules does the text search in this dialog follow?  I notice that when it does return data, it comes back with a message like 'Showing top 11 of an estimated 258 matches', so this may be part of why my prior searches didn't show what I was looking for since they didn't make the top X results. We are baffled though as to why my co-workers name searches returned a full list on Monday then Tuesday didn't return the same results.

Any light that can be shed on this would be greatly appreciated.

Thanks,

Jamie.