Linkers, and Crb, please do not give advice if you are not sure of the answer, as both of your answers contain incorrect information.
leave to enter/remain is not automatically curtailed - the UKBA would have to make a decision to curtail the leave of the dependent so to say that the dependent's leave has been curtailed is incorrect.
The 2 years does not start from when the spouse is granted further leave on form FLR(M). A combination of PBS dependent leave, and leave as the spouse of a settled person can be used to make up the two years for the spouse to qualify for ILR. There is no requirement to switch within 28 days but it is better to make the application sooner rather than later.
See
FLR or ILR for my dependent
and
FAQs for ILR - WP/Tier 1/Tier 2/HSMP holders