impossible to delete a three-notes tie

For as much as I tried I could not delete the three-notes tie (see attachment) in both tenor and bass stave.
I've tried the following:
1) I selected only the tie and right clicked - the cut and delete functions were present in the drop-down list but none worked (I would have expected that the "object programming" logic would imply that only applicable functions would be made available/visible at any given point)
2) deleted only one note but the tie reappeared when I re-inserted the note
3) deleted all three notes - as soon as I re-inserted the second note the tie reappeared and it joined when the third note was inserted again
4) I opened INSPECTOR but nothing in there could help
Am I out of options or is there another way to achieve that?
Thanks for help.