Something goes wrong in the JSON export when scaling bones.

With XY scale 1.0 on the pelvis bone, it outputs

"bones": [
{ "name": "root" },
{ "name": "hip", "parent": "root", "x": 15.57, "y": 115.73 },
{ "name": "left upper leg", "parent": "hip", "length": 50.39, "x": 9.8, "y": 1.12, "rotation": -89.09 },
{ "name": "pelvis", "parent": "hip", "x": 1.41, "y": -6.57 },

With XY scale != 1.0 on the pelvis bone (.92 in this case, [edit: also for 2.5]), it outputs

"bones": [
{ "name": "root" },
{ "name": "hip", "parent": "root", "x": 15.57, "y": 115.73 },
{ "name": "left upper leg", "parent": "hip", "length": 50.39, "x": 9.8, "y": 1.12, "rotation": -89.09 },
{ "name": "pelvis", "parent": "hip", "x": 1.41, "y": -6.57, "scaleX": 1.412, "scaleY": -6.579 },

It seems like it's writing the x, y values to the scaleX, scaleY values

[EDIT]
Sorry, just found this topic on the same bug
viewtopic.php?f=9&t=2179