SE06 modifiable changes effecting on both clients in DEV server

Dear All,

In DEV server i have created one more client apart from 300 , i have created 500,

copied the profile SAP_CUST from PRD server , customising data copied sucessfully.

as per requirment i want 500 to be in modifiable status and 300 non-modifiable.

but when i changed the status of client 500 to modifiable 300 also getting changed to modifiable. and when i change 300 to not modifiable 500 also getting changed to non-modifiable.

i have checked by both the clients open in SCC4 and also by locking.

Kindly suggest.