Wraith Ult can't be cancelled while on zipline.

[Owen CMYK]

If you press 4 on Wraith, it'll enter a mode where you select your target. If you hop on a zipline, the ult icon will still be illuminated, but the screen effect will be gone. You cannot cancel the ult while on the zipline, and when you get off the zipline you'll still be in the ult.