For those unaware, our dice system can roll fudge dice with df.
The bug is that df is the only correct way to roll fudge dice. dF, with the F capitalised, just defaults to "1":
Princess Bubblegum rolls
10dF verboseand gets10! (1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1)
This means Fate's 4dF always results in 4, which is the 1%-of-the-time max roll. I had a Fate adventure earlier in which I did this completely by accident. If I hadn't remembered this coming up in chat once, I would've continued to do this quite a lot!
Both 4df and 4dF should roll fudge dice, i.e. it shouldn't care whether the F is capitalised.