This isn’t a feature so much as an overly generous use of an underlying behaviour in the text editor. Basically if you put your cursor on a line and then scroll to another area of the text so that the cursor isn’t on the screen and then start typing, this is precisely the behaviour you’ll get: the line you are typing on is scrolled to the middle of the screen so you can see what you’re doing.
The problem is that it is triggering too early and too easily. We hope to have it fixed for a future upgrade, but like I say it’s a bit tricky since it’s technically a glitch in the underlying toolkit.
If you’re running into it with great frequency, consider using the Highlight current line option in the upper-left corner of the Editor preference pane (you can change the colour of it in the Appearance pane, under the Editor section of the customisable colours section).