word based diff on TortoiseMerge is not consistent

[Ioannis Cherouvim]

Hello. I use the latest version of TortoiseMerge (from installing the latest version of  TortoiseSVN) on windows 7.

I understand that svn is line based so even if 1 character changes, the whole line changes. But TortoiseMerge has this useful UI feature where it highlights changed words.

Sometimes though it highlights the whole line which is a bit confusing.

Assume this committed file:

foo: {
    title: "1111",
    header: "2222",
    content: "3333"
}

If I change it to the following:

foo: {
    title: "1111",
    header: "1 2 3 4 5 6",
    content: "1 2 3 4"
}

and use TortoiseMerge before commit to view changes, then it highlights the whole 3rd line changed (header: "1 2 3 4 5 6",), but only the "1 2 3 4" in the 4th line which is correct.  A screenshot to better showcase this can be found at https://i.imgur.com/HrjQK4C.png

Is there an explanation for that behavior? I assume it has to do with a threshold or amount of words? Could this be configured somehow?

thanks