As I don't know the interns of this dimmer it might switch when the alternating voltage (and therefore the current with resistive loads) crosses zero. To detect the phase (crossing 0V will occur at 0° 180° and 360° which is again 0° - you might want to look it up here: http://en.wikipedia.org/wiki/Phase_(waves) ) and the type of load (e.g. inductive loads delay the flow of current depending on their inductance and the frequency in relation to the voltage. I could not find a text on wikipedia describing that so here's a plain image: http://people.sinclair.edu/nickreeder/eet155/PageArt/phaseInductor.gif
To detect the type of load it has to observe the mains line for a short period of time without regulating it.
The issue does not occur on light loads because most dimmers can handle inductive, capacitive and resistive loads quite well on low power levels.
By letting the dimmer "cool down" you may erase its short term memory so it has to resynchronize every time you switch it on.
Again: As the internals of this dimmer (or better: the two) are not known I can't provide a better answer. A newer hardware revision usually improves the product. Also chinese manufacturers tend to produce lower quality products as seen here: http://hackaday.com/2012/08/15/buying-cheaper-electronics-and-not-saving-money/
If the bulb fits in the base, it is the right kind. It could be a problem with the fixture, but it could be anything else along the line as well, a bad switch, bad connection somewhere, faulty insulation, chewed by rodents, etc. RCDs are very sensitive, it doesn't take much current leakage somewhere to set them off.
If a careful visual inspection doesn't reveal anything, about all you can do is take various components out of the system until you find the one that was tripping the RCD. For instance, test the fixture by removing the wiring and connecting the wires to a simple keyless base with a light bulb installed. If the RCD does not trip and the bulb illuminates, then you know the fixture is at fault.
If the RCD still trips, then the fixture is not at fault. Next try taking the switch out of the system by wiring the switch wires together so that you have an unswitched circuit. Test again. If the RCD still trips, identify intervening junctions and connect your test light at each one, starting at the switch and working back towards the distribution panel. You will eventually make a connection that does not trip the RCD. Then you know the bad section is immediately upstream from the successful connection.
I've left out many safety details here in order to outline basic trouble shooting. If you are at all uncomfortable working on building electrics, do not do any of this, find someone that knows what they are doing. Also, if you have an older UK ring system, these confuse most people, you need to find someone familiar with this rather unusual arrangement.
Best Answer
That looks like an integrated LED can retrofit fixture (a close match for some of mine - I see the supply converter screwed into the original can socket) and you replace the whole thing - there is no removable bulb.
If you enjoy tinkering the LEDs are probably fine, and the driver circuit is probably dying, but that's strictly "reuse LEDs for your low voltage projects" not "do a home replacement and return it to service at line voltage with unlisted parts and repairs" - for fixing the light in this location that's attached to mains voltage, just buy a new LED retrofit with all the proper listings so that you don't void your insurance...