Input Lag when Anti-Aliasing Enabled in Mod Launcher?

When I play the game, I get input lag with the buttons, and the mouse lags behind where I move it, and the game's framerate slows down, but only when I have anti-aliasing turned on in the launcher. Is there some way I could fix this? Or is it an issue with my computer? With AA turned off, it works fine. Is there another setting I need to enable?

Have you tried all AA settings starting with 2xMSAA then going too 8xMSAA. The only other thing i could think of is maybe changing the frame limiter options and seeing if that helps some, the only other thing i could think of is maybe going into the developer settings and then going into graphics and then try turning on VERTICAL SYNC as that should make the game stay synced to your monitiors refresh rate, other than that like you said it could be your computer but without knowing your "computer specs" it's kinda difficult to track down the issue.
i hope this information helps anyway, i try what i can too at least help.

I have tried it with 2x, and it works significantly better. I have not tried changing the frame limiter options or VSync, I will try them now.

ok ok let me know how it works out, If it doesn't work out well then i am not sure what else i can suggest you try except a combination of various settings untill something works.

I tried turning off the frame limiter and it did not help, but how do I access the developer settings to enable Vertical Sync?

ok so go into the launcher then click on the "developer tab" then turn on "Debug test" then click on the "Mod settings" then click on "Graphics" and vertical sync is the third one down and the click on that and press ok.

I tried VSync, but what I found helped the most was to lower the frame limiter (for example, to 30fps), but I will try different combinations and will see what works. If you have any ideas, please let me know.

yes i will try and help anyway i can, well to the extent one can of course.
the only last thing i can think of is for you to download the latest graphic card drivers, i know this is probably the first thing you probably have tried or at least THE LAST thing you want to hear believe me.
But still it is worth a try fresh installing graphics card drivers and then giving it another go.

Wait, there is AA in the launcher? i never knew that! where is located tho

the AA is located in the "GENERAL" tab in the launcher and it is the first option then once you tick to enable it click "MOD SETTINGS" on the right and then you can change the AA mode
2xmsaa
4xmsaa
8xmsaa

But as tungsten8 has said it was making the game lag so i guess it depends on what you have hardware wise in your computer.
So you might wanna mess around with the settings untill something works for you.