I am renting a small flat that has about 20 downlights throughout the property. It looks like there's a random collection of whatever halogen downlights the previous tenants could find. Some are not working, so I'm replacing them all with new LED ones. I've just replaced the 8 in the kitchen/dining room. There are 2 light switches - 1 switch turns 5 bulbs on, the other turns the remaining 3 on. When I turn on the 3, one of them flashes, roughly once a second. I've tried 2 different brand new bulbs, and the behaviour is the same. All others turn on normally as expected. What could the cause of this be, and how can I fix it? For reference, the bulbs are all MR16 GU5.3 bulbs, 2.9W with 230 lumen output.