Pasting Path Effect onto object doesn't preserve fill/stroke properly

Partially fixed

See #623 (comment 325534764) for existing issue

Steps to reproduce:

• open Inkscape
• With pen tool (shift+F6), in regular bezier or spiro or bspline mode, shape to "None", draw a path. I'll be referring to as "target path"
• With pen tool (shift+F6), regular bezier mode, shape to "Triangle in", draw a two points path. I'll be referring to as "source path"
• If not selected, select the source path, copy it (Ctrl+C)
• Select the target path and Path > Apply the path effect

What happened?

• Unwanted path effect applied to the target path
• Source path also modified, with the same unwanted path effect

What should have happened?

• Pasting path effect from a source path to another path (target path) is expected to apply the same path effect.
• Pasting path effect is never supposed to modify the source path.

In Inkscape 0.92.4 everything works fine

Inkscape Version and Operating System:

• Inkscape Version: 1.0beta2 (418fe521, 2019-12-12)
• Operating System: windows 8.1 64x

Example file

Here is a sample file. Please note that the observed effect goes beyond what is described above : all the copies (no clone at all) of the source path effect are modified ! Same results with each of the rectangles.

Thank you for listening.

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