How does Batrider's tether-break and napalm work WRT his firefly ability?

Two questions in one here guys, let me know if better to split them out:

1. If Batrider has ult'd someone and lasso'd them, under what circumstances does the lasso break? I ask as on various occasions I've seen it break, but it appears to be inconsistent, so wondering how that works. One example I've seen is if Bat uses a force-staff it can break, but sometimes it doesn't break.

2. If Batrider has applied stacks of sticky napalm to a hero, and then the hero takes damage from his firefly AoE ability - does the firefly DPS increase with napalm stacks? For example - if Bat has level 1 firefly (20 DPS) and level 1 sticky napalm (extra 10 damage), then does a hero with 1 stack of sticky napalm take 30 DPS or 20?

Thanks!