Why do my UITableView cells not update correctly?

Question

I have this weird issue and I can't seem to find out why.

Here's the deal; I have a UITableView with some cells which the data comes from an array, there is a button in my cell, once pressed it displays new rows which are part of the cell. The cells are a dark shade of colour, like everything else in my UITableView, I have triple checked the storyboard for any white colours, but still my cell displays a small white line to the left of the separator, the line disappears when the cell goes out of the viewport on the top but appears again when the cell went out of the viewport on the bottom.

Here is what I see once I press the button to show the other rows, and also what I see when the cells were scrolled out of the viewport at the bottom.

And here is what I see once the cells were scrolled out of the viewport at the top.

Here is the code for when I press the button.

- (IBAction)onGroupButtonClick:(id)sender {
    UIButton *button = (UIButton*)sender;

    showSubRows = YES;

    [contactList setNeedsDisplay];
    [contactList setNeedsLayout];
    [contactList reloadData];
}

And here is the code for the indented rows.

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    if(showSubRows) {
        subRow *subRow = (subRow*)data[indexPath.section];

        [button setAlpha:0.0f];
        // Fill vars..
    }
}

I hope I have provided enough information.

Thanks.