Problem with MS SQL 2000 and indexes

I have a problem when I use MS SQL 2000 in Delphi 5 (BDE 5.1.1)
I use SQLLinks driver.
The problem is with indexes.
When I create tables all indexes are retreived correctly in
TTable.IndexDefs, but after I execute any operation on any table then new
indexes appeared
For Examle: _WA_Sys_Firm_503BEA1C, where "Firm" is field from a table.
And if table has Foreign keys - these indexes disappeared.
Where is a problem?