When using the Moodlalis set (I installed just the icons under moodle/pix) we get something like the attached screenshot.

The reason is that core Moodle expects 12x12 px here (tiny icons) but the Tango ones are 16x16.

The different results are because of inconsistent CSS.

I'm not sure what the best solution is.

1) Do we always use 16x16 and resize them in standard themes?
2) Produce 12x12 versions in core?
3) Always display them as 16x16? (this looks a little big to me)