Pencil Tool deletes hydrogen atoms when bond order are changed

[grsousajunior]

Avogadro version:

• Avogadrolibs: 1.91.0
• Qt: 5.10.1

Desktop version:

• OS: Microsoft Windows
• Version: 10.0.19041.572

Describe the bug
When changing bond order from ethane by clicking on C–C bond using Pencil Tool, hydrogen atoms from neighbor carbon are deleted.

To Reproduce
Steps to reproduce the behavior:

1. Go to Pencil Tool
2. Click on screen to add CH₄ molecule
3. Add the second carbon atom to create a ethane
4. Go to Extensions > Open Babel > Optimize geometry
5. Click on C–C bond to change the bond order and the H atoms to second carbon are deleted

Expected behavior
I expected to build an ethene molecule.

Screenshots
The follow gif image shows step-by-step what I'm doing.

Additional context
During installation, the Wizard show up this error message:

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[ghutchis]

This seems to be fixed in HEAD so I'm closing this one.

[ghutchis]

Just verified it - I'll see what's happening. Seems somewhat intermittent on my computer.

[ghutchis]

I'm going to close this one in favor of #678 as a "master issue" - the adjust hydrogens code is buggy and sometimes fails.