Weird inputs using a PS4 pad

First, please forgive me if this is not the right place to ask, I wasn’t sure.

I’m usually using a stick, but since the inputs are easier in SFV, I’ve been trying to learn using a pad too. I was doing jab/command-throws in the training room with Laura, and I kept getting fireballs instead of her command throw. Since her command throw uses kick buttons, and the inputs only showed one jab, it was weird, so I stopped doing the kick, and kept getting fireballs. What I’m doing is crouch-jab, f, df, d, db, b, and I’m getting both the jab and the fireball. Is there some weird buffering happening ? I don’t have any problem doing jab/command-throw with the stick, and I’m not getting any fireballs.