var obj = jQuery.parseJSON( lines );
this will produce an array.
... .append( obj + '<tr ...
this will convert the array to string that looks very much like this: '...</tr>,<tr ...'
before appending your new row.
If you want to concatenate the elements of the string client-side (why not do it server-side?), you can use the array method join
:
... .append( obj.join('') + '<tr ...
solved Ajax array showing comma (,) in IE [closed]