TRIAC Dimming Modules - 60Hz Module on 50Hz Supply
I have now worked on several products that incorporated triac controls. Cost was the driving force when selecting their features and functions. The cheaper product's microcontroller simply did not have enough memory to support dynamically selecting 50/60. Therefore the software was hard coded and two market specific software versions were made. 

The more expensive product needed a micro with more inputs and outputs. This gave the micro the side effective of having more memory. The greater memory gave the ability to code dynamic 50/60 support. 

Triac's have a minimum on pulse value to ensure that they turn on. The software that I have dealt with slides that pulse around to change the dimming. The problem can come from how often that pulse is synchronized with the zero crossing. If it's every half cycle then the wave form is symetric and there won't be any problems until very low dimming is needed. In the scenario the pulse will slide over top of the trailing zero crossing false triggering the triac for another half cycle. This would cause flickering but only when a very low dimming state is reached. 

If the synchronization happens every cycle then the waveform won't be symmetric between the first half cycle and second half cycle. This will cause flickering as soon as dimming is induced.