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Happens sometimes to me, but I'm fixing it with closing the keyboard, tapping to times onto some word, then the navigation wheel appears & can be moved. Afterwards you can just easily open the keyboard again.

That's the problem: Deactivating soft tabs and activating TextExpander leads to an replacement of four spaces to one tab..
For me it's also not possible to reproduce it everytime. It happens often, when I restructure my HTML-code. When I'm having an element at the beginning of the line and put in 3 spaces, then somethimes the whole line jumps at the end of the line before and removing the last 2 chars.
You're right: It's the TextExpander, which was activated, but not installed.
Another thing, which happens for me: With activated (not installed) Textexpander I'm putting in 4 spaces (Softtab) at the beginning of the line and then the cursor jumps back three spaces (after the first one).

Since I'm not using Text Expander, I deactivated it now and everything's working like a charme. I'll submit another "bug" in a minute :)