NULL characters and sorting

[Paul Looney]

One of my customers had a problem displaying all of their archived  
orders.
There should have been 16,020 archived records but only 3,879 were  
showing up in the list.
They could "Find" the missing records and navigate to them with the  
"Next" and "Previous" commands.
Other programs in the system would show the entire list.
In approx. three years on the market, no other customers using the  
same system had reported this problem with their data.
I started checking the contents of variables in the appropriate  
handler and discovered there were the proper number of records just  
before a sort by column. After the sort, records were missing.
Phil, the Great, Davis - Wizard of West Linn - suggested checking for  
and removing NULLs (because they terminate a line in C). They were  
131,023 NULLs in the pre-sort variable.
When I removed them before the sort, the number of listed records  
jumped from 3,879 to 16,020.
This leaves some questions:
How can 131,023 NULL "characters" reduce the displayed "lines" by  
12,141?
Are there other characters that should be trapped before a sort?

This problem was verified on many computers running OS X - both Tiger  
and Leopard, from G4 iMacs to the most recent  24" Intel iMac.

Here is the code that does the sorting:
sort lines of tDisplayRecords ascending by item tSortColumn of each

Sorting ascending or descending made no difference, the selected sort  
column made no difference.

Your insight is appreciated.
Paul Looney