Duplicating or reopening file with LPE Offset changes size if non-mm units

Summary:

Inkscape doesn't storage the LPE Offset properties permanently for every object. Some both object and document changes can corrupt the user-defined values.

Steps to reproduce:

• Open Inkscape
• Change Display units to px (in Document properties)
• Create a circle.
• Set a Offset LPE.
• Change its units to px, and set a non-zero distance

then...

(First issue)

• Duplicate it.

(Second issue)

• Save the document and close it.
• Reopen the document.

What happened?

Offset width has been changed in both occasions.

What should have happened?

Should have the same configurations as original/before closing.

Version Info:

- Inkscape Version: 1.0 (4035a4fb49, 2020-05-01) from MX Linux's Test Repository
- Operating System: MX Linux
- Operating System version: 19.2