Almost every dash in the game has this issue. If you get CCed mid-dash by anything other than displacement, the effect will not apply until you finish traveling. This used to be a large issue on Kalista before she got heavily nerfed, because her perma-dash made her effectively immune to slows, and highly resistant to most other forms of CC (she still has this problem, to some extent).
To a larger degree, the state of mobility and crowd control now hasn't really evolved that much since the start of the game, and both systems have a lot of issues with both coding and design that haven't been properly addressed. One of the likely reasons we experienced knockup creep on a string of champion releases, for example, is because displacement carries a lot more clarity than other forms of hard CC, and actually interacts properly with dashes. Mobility needs to be properly affected by crowd control at all times, and CC itself needs to have both its clarity and interaction with other game elements brought to modern standards (people with Tenacity can still Flash out of Soraka's persistent silence, for example).