non-standard pipeline, state calls or set flags cause driver-level render filtering to fail, most specifically AA settings. Standard OGL deferred rendering is not affected.

solutions;

• use more standard modern game deferred rendering
• add an option for SSAA
• if it is indeed just set states or flags that force-disable driver settings, provide an option to disable these.

this seems to be a known bug since 1.7.2.

side note for those who might not know; in the options file there's an option called 'fboEnable', if you set this to false it'll disable the deferred render and rendering behaves like it did in mc 1.6 and earlier. so ie things like SSAA will work correctly etc.

.13+ note; you can nolonger disable the FBO to switch back to forward rendering, so the above fix nolonger works.