Monsters fly insanely high with upperstab?

Describe the problem. Be as specific as possible!:
When you use Upperstab monster fly at least 3 times as high as normally?

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Is this normal cuz im pretty sure its not O_O

EDIT: lol i just found out it only happens with these monsters but not with any other monsters.
And btw it can reach till the upperplatform by hitting it only once it looks very odd.