Add 1.6.3 bugfix into master.

[n2ygk]

Description of the Change

Update stable/1.6 branch into master.

Checklist

• PR only contains one change (considered splitting up PR)
• unit-test added
• documentation updated
• CHANGELOG.md updated (only for user relevant changes)
• author name in AUTHORS

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.65%. Comparing base (baba2ed) to head (0431aba).
Report is 204 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1086   +/-   ##
=======================================
  Coverage   96.65%   96.65%           
=======================================
  Files          31       31           
  Lines        1763     1763           
=======================================
  Hits         1704     1704           
  Misses         59       59           

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