numapde-get-bib.sh introduces incorrect protection marks

numapde-get-bib.sh 10.1007/978-3-030-50450-2_8 is OK but numapde-get-bib.sh 10.1007/978-3-030-50450-2_8 --merge new.bib introduces a stray backslash into the DOI:

  AUTHOR = {Albi, Giacomo and Cristiani, Emiliano and Pareschi, Lorenzo and Peri, Daniele},
  PUBLISHER = {Springer International Publishing},
  BOOKTITLE = {Crowd Dynamics, Volume 2},
  DATE = {2020},
  DOI = {10.1007/978-3-030-50450-2\_8},
  PAGES = {159--197},
  TITLE = {Mathematical Models and Methods for Crowd Dynamics Control},
}

A similar issues occurs with existing backslashes, as in numapde-get-bib.sh 10.1137/17m1117872, where the publisher entry contains \\& instead of the original and correct \&.