It’s hard to describe this, and I’m not sure whether there’s something wrong with my bike.
Say I’m cycling along a long straight in sixth gear. If I brake enough to slow down rapidly (like round a corner) my bike suddenly acts as if it is in a lower gear (i.e. first gear), then after a few rotations of the pedals the bike snaps back into sixth. I find this infuriating as I suddenly need to pedal faster temporarily otherwise I will lose my speed.
I spoke to a friend about this but they insisted it was intentional and due to the bike’s “Shimano gear system”, but I haven’t experienced this on other bikes at all (they remain at sixth at all times).
Is there something wrong with my bike? And if so, what?
Edit: Added some photos. It seems to be an Apollo bike from Halfords.