When rolling a die with !! and r#, in this case it was r1, the reroll supersedes the explosion. What I mean is: I roll 10d10!!r1. I roll a 10, so it rolls again. If the number it rolls is a 1 the reroll scraps the whole thing, even though I actually rolled an 11, not a 1. If I roll a 10, then another 10, then a 1, reroll scraps the 21 because it rolled a 1. This is obviously not as intended. My assumption is that the easiest way to prevent this would be for exploded dice to turn off reroll for the duration of that die, or else have reroll figure it out after things have been added up. I don't know which would be easier based on the code, or if it would have to be something else entirely.