Here's an example:
At the moment, the latest entry there is October 13, which would be mistaken to mean October last year (2012), but it actually is October 2010. This applies to all the filters in the activity tab.
As of today:
Yes, at long last there is some indication in these lists when the most current activity is not from the current year. We should've probably done this long ago - goodness knows how often this has tripped me up when viewing folks' profiles - but Alex came back after you posted this, so we had to wait for him to take another break in order to reproduce the problem. /s
The page now prefaces sections of the timeline not from the current year with a header containing the year number. So for instance, the first page of this guy's activity list is currently separated into 4 sections by such headers:
...while the second page starts out with a header indicating the year being continued:
I went with this approach to keep the design as close as possible to what folks are used to; we have several other styles of lists that do contain years, but they tend to contain posts with a fixed set of information in each - so putting the full (or relative) date in a consistent spot isn't as noisy as it would be here.
This change applies to the following pages:
...and the mobile versions of all those pages, which was probably a bigger problem to begin with given the lack of hovertext on mobile:
Thanks to Adam, Nick and Aaron for their help getting this done. And big thanks to everyone who reported this for being so very, very patient.