It all goes back to the beginning of 2010. Though I'd experimented with different characters and scenarios over the first six months of Super Haters, I needed even more change.
I decided to beef up the comic strip with three more panels, taking it to a grand total of six. This would give me a chance to experiment with different kinds of jokes for Destruct-O-Tron and Mind's Eye, hopefully yielding bigger payoffs.
I wanted the first new story arc -- Under Construction -- to feature gags that broke the 4th wall. Specifically, I wanted the jokes to reference the new layout and make fun of the Haters for having trouble adjusting to the additional panels.
In Super Haters #28, the heroes ran into direct conflict with the new reading direction. But these new six-panel strips were laid out vertically, not horizontally... which means that the joke from #28 -- a red arrow pointing readers in the right direction -- doesn't work when transferred to the horizontal layout of SuperHaters.com.
So that's why it's missing! Luckily, leaving #28 out of the reading order doesn't affect the story, and you can always pop over to AudioShocker.com to check it out.