一个奇怪的透明遮罩问题

I make some code like set2D on sprite3d to make sprite3d show on ui.
```
if (_b2D == true)
{
flags &= ~FLAGS_RENDER_AS_3D;
}
```
and
```
if (_b2D == true)
{
meshCommand.set3D(false);
}
```
and it works, the sprite3d show normal on the ui
then I make some normal sprite3d on the 3d layer,

but when i open the ui, the ui's sprite3d show with a transparent mask of the normal sprite3d

who can tell me why?

 

with rendertexture: