Hi Muhammad,
We would request you to kindly click on the "Start new Discussion" link to raise your queries in future instead of the "create new document" link

Regarding this issue, the reason why the price could be changing is that there may be some automatic modifiers getting applied to the line.

After the price changes , navigate to actions>>view adjustments and then check what is the modifier that is getting applied. Then navigate to Pricing>>Modifier form and then query that particular modifier and disable it (by either end dating the modifier OR inactivating it) to ensure that it does not get applied

Hope this helps

Regards
Krishna

As i said earlier i intended to create discussion sorry again..

Thanks for the update i'll try these steps maybe they can help.. 

Regards,

Muhammad Daniyal