SQL Server Bulk Update Changes Column VAlues -

i ran update query on rows (approx. 25k)... update query simple update shown here:

update om_challans set locktype = 'locked', lockactiondate = getdate(), lockactionby = 'query' 

i have not updated other column @ all.

i have trigger keeps history in 'om_challans_history' table, row changes moved history table.
noticed data in 26 rows have been changed 0 automatically query. here sample of mean:

any idea of how possible appreciated

update

here trigger on om_challans table

alter trigger [dbo].[t_createupdatehistory1] on [dbo].[om_challans] after update     set nocount on  if  ((select [status] deleted) '%fielddata%') begin     return end   insert om_challans_history ( [rec_ltr1] , [challan_id] , [locktype], [lockactiondate], [lockactionby], [samplessent] ) /* columns in om_challans table */  select    i.rec_ltr1  , i.challan_id  , i.locktype, i.lockactiondate, i.lockactionby, i.samplessent /* old values of table */     om_challans        inner join     deleted         on             a.sno = i.sno /* primary key columns table */