I tried to reproduce it on 3.1 and 3.2 but it worked fine here (WinXP).
This is what I did:
1) open IDLE;
2) file --> new window;
3) write some text;
4) select with the mouse some text;
5) press shift and keep it pressed;
6) press end;
7) press home;
8) release shift;

I also tried in the "Python Shell" and releasing shift before pressing end and home, but I got the same result.  Shift+end highlights till the end of the line, shift+home till the beginning.