Double-click in your image, and then right-click over the Y-axis (the label “Y-axis” should be visible).
Select “Axis format” from the contextual menu.
Go to the “Numbers” tab and de-select (un-check) the option “Format of origin”.
Now you can adjust the value of “Decimals” (e.g. to “2”) under the “Options” section. Click “OK”.
Click to open a full-resolution version of the image.
Now, as to why the Y axis shows this (very small) number when it should be simply zero, I don’t know. The axis properties are automatically set so the X-axis should be placed at zero, but the graph somehow shows something else.
This is surely a bug, now it is a matter of finding out whether it has been reported already. If not, please file a bug.
Either way, please post a link to any bugs found or filed in a comment below using the format “fdo#123456”.