@Clition
It is an unintended behaviour (aka ‘bug’) indeed, arising from poor programming implementation when the x4 speed was introduced: however, the devs have decided to label it ‘not a bug’ to avoid having to deal with it. It is not the first nor the last time that such an approach is used to justify inconsistencies (e.g. the Great Maw+Copycat ‘non-bug’ [Not a Bug] Great Maw + Copycat bug ).
PS: I have replied in this thread to try and avoid having this comment deleted by the ‘Bug Reports Section’ Biased Police.