The mouse has to be moved after selecting a path,
before it's possible to select a line segment.
reproduce the problem by doing the following:
1. draw a path with two nodes and deselect it
2. change to the "edit paths by nodes (F2)" tool
3. move the mouse over the path
4. don't move the mouse while pressing the left mouse button once,
the path becomes selected
5. when pressing the left mouse button again,
one expects the line segment to get selected,
but nothing happens
6. if one moves the cursor 1 pixels, the cursor doesn't change,
but if one now presses the left mouse button,
then the line segment gets selected and a hand icon apperas below the node tools cursor
7. deselect the path (click away from it) and follow steps 3 and 4,
if one now moves the cursor 2 pixels, then the hand icon appears below the node tools cursor indicating that it's possible to select or drag the line segment, and if one presses the left mouse button the line segment becomes selected.
8. if one selects the path (without moving the mouse) and starts left mouse button dragging on the path then the selection rectangle (rubberband?) gets drawn from the mouse, as if nothing was under the cursor.
To move the cursor 1 pixel at a time i turned on mouse keys,
in linux mint 15 cinnamon the setting is under:
system settings > universal access > pointing and clicking > mouse keys
i seam to remember a similar feature being available in windows.
Tested with:
inkscape_0.49~devel+12830+12~ubuntu12.10.1_i386.deb
on linux mint 15 cinnamon 32bit
Confirmed on Crunchbang Waldorf (a Debian stable based distro) with Inkscape 0.48.3.1 and trunk revision 12832.