Switching off dimmable LED flashes then switches back on
This is the dimmer malfunctioning.  Simple as that.  

This type of problem can usually be managed in one of two ways. 


have one of the bulbs be incandescent
have a properly safety-listed "resistor block" (read: capacitor assembly) wired in parallel with the lamps.  This mimicks an incandescent bulb in the way we aim to accomplish above, and uses less power, and doesn't burn out.  In the States there's one I'm fond of recommending, made by Lutron and UL-listed, but it's not going to work in the land of square light switches. Consult your major dimmer vendors' catalogs if they make a similar module. 


Make sure it is be BSI-listed, TUV, ETL, CSA, UL, one of the proper testing labs who is recognized in your country (an increasing number are, due to trade treaties). Chimazon will cheerfully sell you dangerous rubbish with a CE or CCC label.