Thanks for the report. Sorry for the delay, since I don't often check here. Your best bet to contact me is via Facebook or Youtube. You can find links at https://fs.mantrid.net
You are indeed correct, that the boolean there should be false. However, it's only a collision, so the only effect is has it that things (like logs, players, bales, and whelks) won't correctly fall in the middle of the tub, due to the invisible barrier. It has no effect on fill triggers. I've just re-checked and tested the fill trigger, and it is working perfectly (stays with "Unload here" option in the menu, and also doesn't interrupt on-going filling, as I drive underneath a silo on cruise control at 1km/h).
If you're still experiencing this problem, please let me know which map (and location) or mod it's occurring with, and ideally provide a video or screenshot. You can most easily contact me on Facebook, since it relentlessly lets me know if I have an unread message. Alternately, there's an email address listed on the Youtube about page, or you can drop a comment on a video and I should see it.