Not reproduced with Inkscape 0.91 r13725 on OS X 10.7.5 (locale: en_US.UTF-8): the 'Measure path' extension produces the same expected result if applied to a selection of multiple lines as Inkscape 0.48.5 (each path is measured and labeled separately and correctly).
Please attach a test case (Inkscape SVG) file with paths which reproduce the reported issue.
Which locale settings and menu language do you use?
Not reproduced with Inkscape 0.91 r13725 on OS X 10.7.5 (locale: en_US.UTF-8): the 'Measure path' extension produces the same expected result if applied to a selection of multiple lines as Inkscape 0.48.5 (each path is measured and labeled separately and correctly).
Please attach a test case (Inkscape SVG) file with paths which reproduce the reported issue.
Which locale settings and menu language do you use?