When dropping closing duties, somehow partial dropping causes full dropping

[chrisjwelly]

(I don't really have much time to elaborate now but here's the gist)

E.g. I have a duty from 4pm-9pm on monday. If I drop (in my case: swap) my 4pm-5pm slot, somehow my "number of hours" is correctly reflected as one hour less, but on the timetable I get the entire duty dropped

Expected: the 4-5pm duty is grabbable, and the 5pm-9pm duty is untouched.

Edit: The result of this is that all the 5pm-9pm duties become "invisible". They are still there, but it's not dropped even though it is as if it is dropped. If I grab my 4-5pm duty, all's gud