自定义tableView标头会导致显示单元格边框

I changed the section header by creating my own view of 23 units high. For section1 you will see a border for the cell on top of the section header bar. The border on top of the section1 header bar only shows when i make a custom view for the header, but doesn't show when i use the default gray section header view. Any ideas on why this is?I changed the section header by creating my own