Hi most likely you have a highly inductive load such as fluorescent light or halogen downlighters? if so change switch for good quality type rated for inductive loads or try to find one with a 10A current rating on it,.
The blue flash is the contacts arcing due to a slow-break action, it will only get worse with age/use so don't leave it too long, I have seen holes burnt through to the front of switches due to thisregards SPARX
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