Comment 2 for bug 611649

The "added transparency and size" is the filter effects region and needed to not cut off the any edges of applied filter effects. This is intentional - otherwise the drop-shadow could be cut off from exported bitmaps (see bug #168349 and duplicates about cut-off blurs without a better bounding box calculation for bitmap export).

<http://tavmjong.free.fr/INKSCAPE/MANUAL/html/File-Export.html#id4336766> describes how to use hidden rectangles to select an export region for bitmap export, if you need to cut-off filter effect regions arbitrarily. You could also manually edit the extend of the region in the filter effect dialog (in the Tab 'Filter General Settings' at the bottom).

Proposing to close as 'Invalid' - with regard to the dimensions of the current selection for exporting to bitmap.

Otherwise maybe the report could be turned into a feature request for the 'Shadows and Glows' filter effects extension to calculate the filter effects region more tightly based on the actually entered parameters for blur radius and offset, instead of always using fixed dimensions of 1.5 x 1.5.
But note that there will always be an enlarged selection frame for objects with a drop shadow by nature of that effect.