[rek'sai] ult channeled with broken tunnel

during a game on twisted treeline, i was playing against a rek'sai and we'd stood the three of us on her tunnel and collapsed it only for her ult cry and beam of light to appear onto the collapsed tunnel after we'd just destroyed it, causing her ult to successfully channel and she appeared at that spot as if the tunnel was still there. this seems like a bug, i'm wondering if there's some kind of slight lenience for the amount of time after, as in if she clicks on the tunnel right before it gets destroyed that it still counts? i thought she wasn't able to teleport to collapsed tunnels, i was under the impression it would cancel her ultimate.