All last winter (2012 to 2013) and this winter (2013 to 2014) up until today I've had to put up with my front lights turning off every time I brake on my winter bike. This is due in part to fork judder induced by a severely knackered headset: it has needed replacing for two years now, but last winter I couldn't even get my forks out of the frame, this winter I could, but only to afford to lavish the bearings with huge amounts of grease, not to replace them. Some of the blame lies with the abuse and drops my lights have received as "family torches for pony jobs" which has made them more prone to turning off under harsh vibration than they should be. But most of blame lies with the brake pads which should have been replaced as long a go as the headset, but due to the general nonsensicality of my life haven't been replaced until now; the problem being that since it's fixed gear, I haven't needed to replace them and so the £3.59 has gone elsewhere.
Anyway, somehow I've managed to replace them this year and I can now brake AND see at the same time. Woohoo!