Here without wrong encoding:

SC1 ):
1) plant a WP via mouse → path from WP to mouse
2) press undo key → WP is deleted, you have a path from ex-WP-position to mouse

SC2 ):
1) click and plant WPa → path from WP to mouse
2) click and plant another WPb → both WPs (a and b) connected, path fromWPb to mouse
3) press undo key 3 times → WPb disappears, still path from WPb to mouse
4) click on WPa → path from position of WPb to WPa, however WPb doesn't exit
anymore.
(optional: 5) save and reload the map → path from WPa to tile x=1 y=1, however
no WP there)