C# / Sql Server 2008 INSERT int value grows automatically to 1000000 -

i had strange problem occured 1 time in sql server 2008.

i work in .net web application (c#) , use sqlcommand access database , execute queries. process following:

1. i have view me maximum number existing in specific table:

   select max(number) maxnumber mytable

2. i maxnumber in variable and, variable, execute insert in mytable maxnumber + 1. that, have maximum number logged in mytable

it worked since 1 time, week ago, when, suddenly, saw maxnumber passed 134200 1000000 !

i investigate code , there no way reason of behavior. inspected logs of web server, no logs of bad insert throwned.

i looked logs of sql server i've found no logs of error...

what suspicious number passed "common" number (134200) "specific" number (1000000). why 1000000 ? why not 984216 or 1000256 ?

is there experienced same problem ?

thanks help.

edit - 2014-12-23:

i analyzed further problem , seems occurred when restored backup in preprod environment.

i explain: have preprod server have sql server instance (preprod) , have prod server have sql server instance (prod), backed every day, on same server.

when want test effective datas, restore prod backups on preprod databases:

restore database preprod disk = '\\prod\backup\sql\prod.bak' move 'prod' 'e:\bases\data\preprod.mdf', move 'prod_log' 'e:\bases\data\preprod.ldf', replace 

the problem occurred same day restored backup. "1000000 row" appeared @ same moment of restore, on prod database. there possibility it's linked ? prod server overwhelmed restore command executed preprod server, , it, eventually, crashed insert request occurred @ same moment ?

thanks advices

the thing can think maybe getting maxvalue executescalar method without casting result proper datatype

var max= cmd.executescalar(); 

and

max= max+1; 

otherwise saw version of sqlserver may receive incorrect values when using scope_identity() , @@identity

refer here bug fix, should update sql server 2008 r2 service pack 1