JavaScript function written on content page is interfering with Buttons of Master Page in ASP.Net

Hello Sir

i added loading popup on my Home page linked with masterpage, i am having login button at the top of master page, when i click on login, popup is visble with login, and i enter details and click ok, the popup of loading which i added in my homepage gets visible, why its happening as i put my loading on home page not on master page..please help...