Steps to reproduce:

1. Enable the Zoom accessibility feature (System Preferences > Accessibility > Zoom > check "Use scroll gesture...") with zoom following text cursor (check "Zoom follows keyboard focus")
2. Open a document in TextMate
3. Zoom yourself in (⌃-scroll up), preferably as much as possible to really experience this bug
4. Move cursor to beginning of any line (⌘←), and then try moving up/down at the beginning of the lines around (↑, ↓), or try to go to the previous line (← twice) and back (→ twice)

Expected Results:
When text cursor is at beginning of a line, Zoom follows (jumps) to the beginning of line, displaying text cursor.

Actual Results:
When text cursor is at beginning of a line, Zoom follows (jumps) somewhere in the middle of the line, between this line and the preceding line.