I'm trying to cancel Jago's Tiger Fury into Shadow Laser Sword, but it always comes out as Shadow Endokuken. I'm looking at input display and my inputs seem to be right. What's going on here?

I tried it myself on a pad, and couldn't manage to get shadow laser sword, which really struck me as odd. To verify, I plugged my stick in, which is my preferred method of playing, and I was able to get shadow laser sword every time. Weird!
Turns out what's actually happening, upon further inspection, is if you finish your DP motion with a forward input, it doesn't matter what punch special you try to input (shadow DP or shadow laser sword), you will ALWAYS get fireball. I think it's because the game has "queued up" fireball as the next input you performed (because you went d, df, f at one stage), so it looks at that, rather than where you pressed the punch buttons. If you do your DP motion as a strict f, d, df without ever reaching forward again, then wrap QCB and press two punches, you'll get laser sword every time.
I think this is actually a bug/unintended behavior of the input system, but the devs have stated on other occasions that changing the input system to fix issues is not likely going to happen soon because the possibility for catastrophic bugs to enter the game is too high. So if you're looking to do this (for example, to make a DP safe on block), you'll have to either clean up your inputs so your DP is perfect, or look to another alternative, I'm afraid.