sv650 brake help

[bagger]

on the way from work earlier while heavy braking there was several loud bangs and the brakes were on and of rapidly(at first i thought the disc had broke)but when i had a look around the diaphragm had been pulled/distorted into the reservoir?
i know the pads are low and need changing but does anyone know why this happened?
should i worry? i opened the resevoir and put it back correctly(it had basically turned inside out) the fluid level is fine
cheer in advance
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sv650s,cb350s

[TUG]

The diaphram inside the master cylinder fluid pot moves down to keep air gap to a minimum, as the piston moves more out as the pads become warn the level will drop to indicate pad wear or fluid loss.

The banging i'm unsure of, but i suggest you sort your brake pads out ASAP as tyre and brakes keep you safe.
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Haz ER-5, innit!