I do have a problem with saving my print-composition into PDF/SVG-Format (haven't checked image export yet, but I think the problem would be the same).
It turns out the measurements given for sheet size do not match the exported file: E.g. I'm trying to save my plan on a Din A3 (297,0 mm x 420,0 mm) sheet, PDF format. The file created by QGIS measures 297,0 mm x 420,2 mm, which might not seem much, but causes "one-dimensional"-distorsions, as the whole length of the plot is stretched by this 2 mm, within the plan. This in the end makes my plot to not fit the given scale, which is crucial.
Anyone with the same problem and a workaround? It does not help reducing the sheet size within QGIS by 2 mm, then it will magically add like 1 mm, or sometimes reduze it by the same. Also direct printing (could not acutally print it this way yet, but printed it into a PDF-printer) does have the problem.
Currently working with 2.14.1, double checked it with the newest version, same problem.
Could be, of course, that the sheet size does not cause the distorsions in the later print, so that there exist 2 problems: Wrong Sheet size given by QGIS, and (a non-QGIS-problem) with printing. Seems unlikely though.