Lee might be intentionally leaving out multi texture support for static entities.
In a typical FPSC map there will be significantly more static objects than dynamic and its really expensive to support multiple textures for all of that because of all the additional draw calls to the GPU.
This is one of those areas where you actually need to develop your work flow to UV map models so you can benefit from the optimisation of using 1 texture (3 if you are using normal and specular maps etc).
I don't really think this is an engine problem. Its a perceived bug which is actually there for a good reason.