[Bug] [Linux][Cross-platform UI] Delete or update user compound

[einhander]

Describe the bug
Added via JSON file compounds, cannot be removed or updated on newly created flowsheets.

To Reproduce

1. Add compound via JSON
2. Load updated JSON
3. See error: Error: An item with the same key has already been added. Key: My_Compound

Expected behavior
Delete button or

Replace dialog to update compound.

Screenshots
If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: Linux 64-bit
• Version 8.7.1

[einhander]

Update. I tested in pure gtk2 enviroment using xephyr nested xserver and openbox as window manager. I work as expected, an update dialog appears. I'm really confused. It still reproducible in other environments.

[einhander]

Update2: It's only occurs in NEW flowsheets. After save, close and reopen saved flowsheet it's work as expected.