Problem in merge in cvs

[ramanuj singh]

Hi,
 I am facing a wierd problem. There is a branch on main trunk i.e. dev 
branch. In this branch different developer create their branches and 
merge their each branh into main trunk after completing their task.
Developers are using Tortoise CVS as their tool. When a developer merges 
his branch after one developer has already merged his branch into dev 
branch instead of file getting update with the another merge get 
overridden by the file of last developer who has merged the file.

Regards,
Ramanuj Singh