Why are the button background images strecthing?

I have an app in which I have a side menu. In the side menu, the rest of the buttons appear fine but two buttons are stretching weirdly. screenshot attached.

This is how I am setting button images.

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{

    static NSString *simpleTableIdentifier = @"SimpleTableItem";

    RearViewTableViewCell *cell = [self.tableViewSideMenu dequeueReusableCellWithIdentifier:simpleTableIdentifier];
    if(cell == nil)
    {

        NSArray *cellView = [[NSBundle mainBundle] loadNibNamed:@"RearViewTableViewCell" owner:nil options:nil];
        cell = (RearViewTableViewCell *)[cellView objectAtIndex:0];
        cell.btnItemSelector.tag = indexPath.row;
        [cell.btnItemSelector setBackgroundImage:[UIImage imageNamed:[buttonUnselect objectAtIndex:indexPath.row]] forState:UIControlStateNormal];
        [cell.btnItemSelector setBackgroundImage:[UIImage imageNamed:[buttonSelect objectAtIndex:indexPath.row]] forState:UIControlStateHighlighted];
        [cell.btnItemSelector addTarget:self action:@selector(btnMenuItemTapped:) forControlEvents:UIControlEventTouchUpInside];
        cell.selectionStyle =UITableViewCellSelectionStyleNone;

    }
    return cell;

}

I am new to adaptive layout. Is it causing issues? On iphone 5s it runs fine but on iphone 6 it is depicting this behaviour. I have added only one constraint (width) to the tableview. The uitableviewcell (custom) i am using here has all the regular constraints of leading space, vertical space, center alignment etc. Any thoughts?

Update: i set the bg color to red and it turns out the two buttons in questions are being resized to much smaller & probably wider view. Why would that happen?

I would recommend you, to use button.image instead of button.backgroundImage. It looks like setting a backgroundImage to a UIButton can't handle the contentMode of your image because it always stretches the UIImage to the same size as the UIButton.

If you add the UIImage just on the property image you can change position of the image inside the UIButton by changing the contentEdgeInsets manually or inside the Interface Builder.

Just in case you want to set an UIImage as well as a NSString for your UIButton, I would create an own class of type UIButton with an UILabel and UIImage and layout them inside the Interface Builder.