Although QCAD asks to restart, any change of the application default Lineweight value is instantaneously.
There may be other reasons why a restart flag is set for this or these set of preferences.
Agreed, on first install or after resetting the configuration a practical value is preset.
What to use as default value is up to you, your firm/organisation or an industry standard if any.
Please attach your drawing or a drawing example.
I suspect that the entities in question have a custom Lineweight or inherent such from their layer.
Refering to the test.dxf drawing attached to: How to get coordinates according to step value - QCAD Script Programming & Contributions - QCAD Forum
I wrote
Regards,
CVH