Sort as integers doesn't work correctly for lines with two integers

Sorting lines as integers (Edit > Line Operations > Sort Lines as Integers Ascending) should produce the following output:
2 3
2 4
2 10
2 20

Instead it produces the following output:
2 10
2 20
2 3
2 4

Namely, after the first value it switches to lexicographic sorting instead of numerical. My Notepad++ version is v6.9.2 on Windows 7,
