PelleS:
I didn't know phase control dimming could be used for leds as well.
"Mind-bending" in terms of the zero crossing matter, dodgy circuits dredged from who-knows-where and somewhat misguided attempts to use circuit simulation software. 
There are better and worse approaches to the circuits in LED luminaires. If they use simple capacitive "ballasts", then their power factor is bad and phase control becomes very difficult; they are generally labelled as "non-dimmable".
If they use a switchmode regulator with a reservoir capacitor (like a computer PSU), then that capacitor charging to the peak voltage resists phase control and again, the power factor is undesirable.
The best design for both dimmability and power factor, is a switchmode regulator without a reservoir capacitor. This simply makes do with the instant voltage at each point in the waveform and behaves more like a resistive load. And leaving out the capacitor is actually cheaper.
I have not yet dissected any LED bulbs (if for one, because they rarely "burn out"!) so I cannot say what circuit they are using. I do however have two failed LED downlights - non-dimmable - awaiting my attack. They have this pattern of lighting almost fully, dimming progressively out, waiting and then "popping" back on. Presumably heat cycling of a switchmode converter IC. That they failed within two years in service is most disappointing.