Issue #9 for
GL_ARB_buffer_storage makes for fairly grim reading, unfortunately...
It's a pity as this could have been the kick up the jacksie that GL's buffer object API really needed, and the issue in question should really have been resolved by just saying "this is client memory, full stop, using incompatible flags generates an error, here are the flags that are incompatible and the vendors will have to just live with it", but it seems another case of shooting too high and missing the basic requirement as a result.