A rocket can only contain 5 EM plants, so I want to cancel the unfulfilled request for 17 EM plants, which I would normally do by right-clicking. However, that actually instructs the bots to remove the 3 items in that slot (which AFAIK is what I would expect from left-clicking). I don't know if this is a bug.
This visually leaves a request for 17 EM plants in place. There is not actually a request for 17 EM plants, as far as I can tell, because bots do not deliver anything to fill that slot. I feel certain this is a bug.
The slot cannot be cleared by left- or right-clicking, but it can it can be cleared by overwriting the slot with another request and then cancelling it before it is fulfilled.
The issue may be related to quality because if I get the bots to remove the 2 uncommon EM plants from the rocket, then issue a request for 20 uncommon EM plants, 2 of which are fulfilled, and then right click that inventory slot, the remaining request is cancelled but the uncommon EM plants stay in the inventory. (This could also be unrelated to quality, and just depends on whether the rocket inventory is full?)