May increases have always happened, just not normally Southeastern.
Quoting the article below:
" the price hike applies to unregulated fares, or those over which the government has no control."
Couple of examples:
Dover Priory - St Pancras this Saturday £30.80
Dover Priory - St Pancras Saturday 27th £31.80
Dover Priory - Canterbury this Saturday £8.50
Dover Priory - St Pancras Saturday 27th £8.70
See also
http://www.manchestereveningnews.co.uk/news/greater-manchester-news/northern-rail-put-up-fare-13010367