PresentModal working weired

[spraveenk91]

I've reassigned the tabbar frame to my required place. When i opened any of content using [self presentmodal...] and when i dismiss it the tabbar frame was moved to top.

Assiging view controllers -

tabBar = [[MHTabBarController alloc]init];
tabBar.delegate = self;
tabBar.viewControllers = viewControllers;
tabBar.view.frame = CGRectMake(0.0, 50.0, 320.0, 430.0);

opening modalview
SVModalWebViewController *web = [[SVModalWebViewController alloc]initWithURL:[NSURL URLWithString:@"http://www.instagram.com"]];
[self presentModalViewController:web animated:YES];

How to fix this?