I believe this to be a bug with Avogadro
Environment Information: Microsoft Visual C++ Runtime Error
Operating system and version: Windows 10
Expected Behavior: The appropriate hydrogen atoms should be added with the Build, Add hydrogen option.
Actual Behavior: Not all hydrogen atoms are added and error message Microsoft Visual C++ Run time library Runtime Error Program: C:\Program Files (x86)\Avogardo\bin\avogardo.exe has stopped unexpectedly is displayed.