Ios7 Facebook Pop：设置UITableViewCell动画时出现问题

我将按以下方式设置UITableViewCell的动画，首先我将其放大以显示更多细节：

[NSObject pop_animate:^{
    cell.pop_springBounciness = 16;
    cell.pop_springSpeed = 6;
    cell.pop_spring.frame = CGRectMake(x, y, width, expandedHeight);
} completion:^(BOOL finished) {
}];

这与预期一样有效，但当我再次尝试缩小它时，会出现一个异常：

[NSObject pop_animate:^{
    cell.pop_springBounciness = 16;
    cell.pop_springSpeed = 6;
    cell.pop_spring.frame = CGRectMake(x, y, width, shrinkedHeight);
} completion:^(BOOL finished) {
}];

这是我得到的例外：

Unable to simultaneously satisfy constraints.
Probably at least one of the constraints in the following list is one you don't want. Try this: (1) look at each constraint and try to figure out which you don't expect; (2) find the code that added the unwanted constraint or constraints and fix it. (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) 
(
    "<NSAutoresizingMaskLayoutConstraint:0x15b5de60 h=-&- v=-&- UITableViewCellScrollView:0x1536f120.height == TransactionCell:0x1536ef50.height - 0.264848>",
    "<NSAutoresizingMaskLayoutConstraint:0x15b5e4d0 h=--& v=--& V:[TransactionCell:0x1536ef50(0.163815)]>"
)

Will attempt to recover by breaking constraint 
<NSAutoresizingMaskLayoutConstraint:0x15b5de60 h=-&- v=-&- UITableViewCellScrollView:0x1536f120.height == TransactionCell:0x1536ef50.height - 0.264848>

Break on objc_exception_throw to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.

无法同时满足约束。
可能下面列表中至少有一个约束是您不想要的。试着这样做：（1）看看每个约束，试着找出你不期望的约束；（2） 找到添加了不需要的约束的代码，然后修复它。（注意：如果您看到不理解的NSAutoresizingMaskLayoutConstraints，请参阅UIView属性TranslatesAutoResizingMaskToConstraints的文档）
(
"",
""
)
将尝试通过打破约束进行恢复
在objc_异常_抛出时中断，以便在调试器中捕获该异常。
中列出的UIView上UIConstraintBasedLayoutDebugging类别中的方法也可能会有所帮助。

我猜原因是因为spring动画，单元格的高度低于0，但是如何避免呢