It seems that the kana engine for そ has the incorrect writing.

https://dl.dropboxusercontent.com/u/19549/pics/IMG_5744.jpg

According to my text, it should just be one stroke that looks like the character. Skritter expects two strokes that look nothing like そ.

そ is actually written the way it's displayed on your android app in regular handwritten Japanese. The そ with one stroke that you see displayed in text and on websites is closer to its original historical form, but modern handwriting calls for the そ to be split into two separate strokes.

You'll find the same is true for き and さ, both of which are displayed with 3 and 2 strokes respectively, but actually require 4 and 3 strokes when written on paper.

Keep an open mind when learning anything in a new language. It can be frustrating to see two characters that may not look alike at first but are perceived to be the same by native speakers of your second language. But don't shut down the possibility that there's a long history and a good explanation for why that has come to be too fast. Usually, there's a pretty good reason for the way that languages have developed.

I'd also like to add that while we only display そ as two separate strokes it will still accept it if you write it as one single stroke. The same is also true for both き and さ.

I knew about the difference between the printed き and さ versus the handwritten, but had never seen a different version of そ. Regardless, I cannot get the shorter, connected versions of any of them to work. I'll grant it may be the super-slow 2012 Nexus 7 I'm using. Hopefully I'll be able to test with a faster device later this week.

I'd recommend learning the 2 stroke そ and making a habit of writing it that way. I'm working at a Japanese junior high school right now, and all of my students write そ using two strokes, as well as the Japanese teacher, who has studied handwriting and calligraphy extensively.