Please provide information about your OS and Inkscape version (see Inkscape menu 'Help > About Inkscape').
> 2) try to change it height (or width) which is actually a thickness of a line
- What are the 'Affect:' settings of the select tool?
- Which bounding box mode do you use?
- Any active snap modes in effect?
> even thickness should not change
Whether the "thickness" (stroke width) changes or not depends on the 'Affect:' setting of the select tool ('Scale stroke width'): turn off stroke scaling to keep the stroke width unchanged when scaling a selection of stroked paths/objects with the select tool. For non-technical drawings (artistic drawings or illustrations), the scaling of the stroke width is often preferred when scaling a selection (thus it is the default setting).
Keep in mind that the select tool transforms a _selection_ (one or more objects, based on their (visual or geometric) bounding box), not an object's geometry itself: use the node tool to edit the geometry of simple lines without affecting the stroke attributes, or manually change the stroke width in 'Fill & Stroke > Stroke style' if needed.
With regard to the displacement:
testing on Mac OS X 10.5.8 (i386), with default prefs, stroke scaling turned off, no active snapping:
1) Reproduced with Inkscape 0.48.2: the stretched line is displaced (moved) by the amount of the vertical/horizontal stretch
2) Partially reproduced with Inkscape 0.48+devel r10737:
vertically stretching a horizontal line up (in positive y direction) does neither displace the line nor scale the stroke width, vertically stretching a horizontal line down (negative y direction) still displaces (moves) the line without scaling the stroke width
(same with vertical line: no changes when stretching to the right, displaced when stretching to left)
Please provide information about your OS and Inkscape version (see Inkscape menu 'Help > About Inkscape').
> 2) try to change it height (or width) which is actually a thickness of a line
- What are the 'Affect:' settings of the select tool?
- Which bounding box mode do you use?
- Any active snap modes in effect?
> even thickness should not change
Whether the "thickness" (stroke width) changes or not depends on the 'Affect:' setting of the select tool ('Scale stroke width'): turn off stroke scaling to keep the stroke width unchanged when scaling a selection of stroked paths/objects with the select tool. For non-technical drawings (artistic drawings or illustrations), the scaling of the stroke width is often preferred when scaling a selection (thus it is the default setting).
Keep in mind that the select tool transforms a _selection_ (one or more objects, based on their (visual or geometric) bounding box), not an object's geometry itself: use the node tool to edit the geometry of simple lines without affecting the stroke attributes, or manually change the stroke width in 'Fill & Stroke > Stroke style' if needed.
With regard to the displacement:
testing on Mac OS X 10.5.8 (i386), with default prefs, stroke scaling turned off, no active snapping:
1) Reproduced with Inkscape 0.48.2: the stretched line is displaced (moved) by the amount of the vertical/horizontal stretch
2) Partially reproduced with Inkscape 0.48+devel r10737:
vertically stretching a horizontal line up (in positive y direction) does neither displace the line nor scale the stroke width, vertically stretching a horizontal line down (negative y direction) still displaces (moves) the line without scaling the stroke width
(same with vertical line: no changes when stretching to the right, displaced when stretching to left)
Related: /bugs.launchpad .net/inkscape/ +bug/706509>
Bug #706509 in Inkscape: “Endpoint of scaled line segment moves”
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