I've posted a working patch at http://forums.technicpack.net/threads/optifine-held-mod-blocks-render-issue.17825/#post-159466
sp614x has been informed about the bug already. Integrate the patch into technic if you want, or wait for sp614x to fix it upstream.
It's actually a problem with HD texture packs + 4096 block IDs. In the recommended build, ItemRendererHD.class is still stuck on 256 blocks, as is Optifine's version. I think it's fixed in one of the latest releases of Forge 3.3.8.