But the collision disappears if you use Keith Ohara's suggestion to force the tie below the note head.
Yes, I understand this. But isn't the purpose of lilypond to automatize the position of the objects? That's why I don't have to say to each slur, tie and dynamics where they should be, it's angle, if it's up or down.
A lot of collision problems that where issued during lilypond's development where possible to correct manually before, but this kills the title of automatic music engraver that lilypond holds proudly and deservedly.