Too many interpolators, but only when opaque?

So I've been scratching my head over this one for quite some time and it seems like a bug to me;

I have a water shader (which you can check out below). It uses two render textures with Screenspace UVs a normal map using UV1 and a noise texture also using UV1. When I enable lightmapping on the shader I get an error stating there are too many interpolators. Fair enough, I figure Im probably using too may UV channels or something (cant be textures since that only adds up to 6-7 max, including the lightmaps, and it happens even with 2 textures) but then when I when compile the material as transparent, I get no errors at all and everything works perfectly! 

The big problem is that the shader was designed specifically to be opaque to avoid sorting issues, and now im stuck as to how to solve it!

This must be a bug right?

Here's the shader: 
Water.shader