Tweak tool: Roughen one part of the selected path removes the roughening on other parts

Steps to reproduce:

• open Inkscape
• draw a circle
• convert to path
• switch to tweak tool
• roughen one side of the circle
• roughen on the opposite side

What happened?

• Gradually, the roughening on the first side vanishes
• Workaround: switch tool, switch back to tweak tool, start again

What should have happened?

• the roughening should not remove what the tool has already done

Inkscape Version and Operating System:

• Inkscape Version: 1.0alpha2 (727140f98f, 2019-07-27)
• Operating System: Linux Mint 19.1