Hi, it seems to work no matter what layer I try, I tried both -1 and 1. See gif:

Ok, sorry I could not help much, but I need to reproduce the problem first before I can investigate what is happening. You could try some kind of preloader for your water layer graphic or whatever it is that blinks. It could just be that the plugin is struggling to load it in time when it also has to load mirror sprite + light sprites, I am not sure.