iOS7以降のUITableViewCellはセルの選択時に上下のセパレータが消えます。
なので消えないようなカスタムセルを作りました。
iOS7とiOS8で確認しました。SingleLineしか動かないかも。

import UIKit

class SeparatorVisibleCell: UITableViewCell {

	required init(coder aDecoder: NSCoder) {
		super.init(coder: aDecoder)
	}
	
	private lazy var separatorNotificationName = "CellSeparatorNotification"
	private var registered = false
	private lazy var separatorHeight: CGFloat = {
		return 1.0 / UIScreen.mainScreen().scale
		/*
		for v in self.contentView.superview!.subviews as [UIView] {
			println("setShowsSeparator: \(NSStringFromClass(v.dynamicType))")
			if NSStringFromClass(v.dynamicType).hasSuffix("SeparatorView") {
				return v.frame.size.height
			}
		}
		abort()
		return 1.0 / UIScreen.mainScreen().scale
		*/
	}()
	
	deinit {
		if registered {
			NSNotificationCenter.defaultCenter().removeObserver(self, name: separatorNotificationName, object: nil)
		}
	}
	
	override func layoutSubviews() {
		super.layoutSubviews()
		
		if !registered {
			NSNotificationCenter.defaultCenter().addObserver(self, selector: "separatorNotification:", name: separatorNotificationName, object: nil)
			registered = true
		}
		
		if let bg = selectedBackgroundView {
			var r = frame
			r.origin = CGPointMake(0, separatorHeight)
			r.size.height -= separatorHeight
			bg.frame = r
		}
	}
		
	override func setHighlighted(highlighted: Bool, animated: Bool) {
		super.setHighlighted(highlighted, animated: animated)
		setShowsSeparator()
		NSNotificationCenter.defaultCenter().postNotificationName(separatorNotificationName, object: self, userInfo: ["max_y": CGRectGetMinY(frame)])
	}
	
	private func setShowsSeparator() {
		println("setShowsSeparator: \(NSStringFromCGRect(frame))")
		for v in contentView.superview!.subviews as [UIView] {
			println("setShowsSeparator: \(NSStringFromClass(v.dynamicType))")
			if NSStringFromClass(v.dynamicType).hasSuffix("SeparatorView") {
				v.hidden = false
			}
		}
	}
	
	func separatorNotification(notif: NSNotification) {
		var y = notif.userInfo?["max_y"] as CGFloat
		
		println("separatorNotification: \(y), \(NSStringFromCGRect(self.frame)) -> \(abs(CGRectGetMaxY(frame) - y))")
		if abs(CGRectGetMaxY(frame) - y) < 1 {
			setShowsSeparator()
		}
	}
}