Normal text line between checkbox lines is always surrounded by empty lines

Steps to reproduce:
1) Create a list of checkboxes:
    * Type "[] First" then press Enter
    * Type "Second" then press Enter
2) Insert an indented line of normal text between the checkboxes
    * Move the cursor to the end of the first line and press Enter Backpace Backspace
    * Type Tab followed by "Some Normal Text"
3) Save (CTRL-S) and reload (CTRL-R)

Expected Behaviour:
Nothing changes

Actual Behaviour:
Empty lines appear before and after the "Some Normal Text" line.

This bug also occurs if the "Normal Text" line is not indented. However if the line is indented, it is impossible to subsequently remove the spurious empty lines (they reappear after a save/reload cycle).

Bug #511270 also seems to describe something similar to this behaviour:
> when you leave and go back to the page, the sub-item is moved one line down

The example wiki file is attached.

Running latest rev (209) using Win32 Python 2.5.2:
INFO: This is zim 0.44
DEBUG: Python version is (2, 5, 2, 'final', 0)
DEBUG: Gtk version is (2, 12, 11)
DEBUG: Pygtk version is (2, 12, 1)