[mankyd]

Rows 3 and 5 are identical.

[tromp]

This rule is easily overlooked in the tutorial, since the example shown can already be resolved using earlier rules (balancing red/blue in columns).

The tutorial must use an example where unique rows/columns is the only way to resolve the choice...

[vlunkr]

I guess I missed this rule. I got into a similar situation and thought there was a bug

[anon4]

Oh, right. But what about the ones on row 1?

[sp332]

Well if you switch the squares on row 3, you have to switch the square on row 1 as well. Otherwise the columns will not have even numbers of red and blue squares.

[anon4]

Oh. It's really confusing to show not only the current mistake but also the mistakes that would be introduced by fixing it.

[sp332]

True. There is only a single solution to each puzzle, so it just highlights all the blocks which don't match the known solution.