Comment 2 for bug 1246550

Patch tested successfully with r12753 and the Knot path effect: finally the switcher symbol is visible again :)

Two notes about the current patch:
1) LPE_ENABLE_TEST_EFFECTS should not be defined.
(users can add the define when running configure (via CPPFLAGS))
2) The helper paths only update once the mouse is moved again, not e.g. on mouse button release.
This delay is unexpected, and e.g. with the Knot effect makes it someone confusing when cycling through the options by repeatedly clicking on the path effect knot (handle?).