> clicking at same place (within 4 pixels I guess) terminates PolyLine etc
That's nearly true: but if I click quietly :-)
for sure not moving my mouse I get very often:
*** Break *** segmentation violation
(but in that case it does not distroy root and its contents at least)
The other observed unwanted effects:
1. root [2] Fatal in <operator delete>: unreasonable size (1084093744)
aborting - and here root crashes completely
2. the first point (and line from it) changes suddenly its position, most
often it places somewhere at left upper position of canvas
Witek