I discovered that if I open a text file which is in archive in Opus and save it, changes are lost because it's saved to temp file.
- create a new empty plain text document
- archive it into zip
- open (with Opus) that text document within archive in for example Notepad
- type something like "test" and save, close the Notepad
- observe that the text file in archive is not updated, hence loss of data
If I do this with for example 7-zip file manager everything works OK (file manager detects change and asks whether to update the changed file in archive).