ios - UITableView cells are unloaded too early after reordering -

i've built in reordering uitableview there's nasty bug i'm experiencing after reordering cells. bug occurs after cell has been reordered: when scrolling table view up, cells visible @ bottom of screen disappear while scrolling. seems if cells unloaded early. happens when scrolling up. when scrolling down bug doesn't exist. cells randomly disappear re-appear when scrolling down once empty space leaves screen. here's screenshot of issue:

i'm pretty sure data source isn't problem because:

1. when reordering cell data source updates well
2. i've checked table view spark inspector , missing cells aren't hidden or empty don't exist, there no cell @ empty spaces are.
3. after scrolling around cells re-appear, cells randomly appear , disappear

it must bug or issue in uitableview, may wrong assumption. maybe has faced problem , can me out ;) i'm waiting answers :)

edit: checked -tableview:didenddisplayingcell:forrowatindexpath: delegate method , cells unloaded , method called, though cells still visible on screen!

edit (2): know issue occurs when table view has header view. doesn't matter if use default header or custom one, whenever use header view bug. when don't use header works fine. thats strange

note: i'm testing on ios 6.1.2