Comment 24 for bug 1782984

Here's what I tried based on my interpretation of your steps to follow:

 1. Boot 18.04.1
 2. Select "Try Lubuntu"
 3. Right click on the "Trash" icon at the upper left, click "Open in New Window"
 4. Repeat step 3
 5. Open the task manager to keep an eye on things
 6. In one of the PCManFM windows (let's call this Window A), click "Home Folder"
 7. Right click, "Create > New Folder", take the default name ("New")
 8. In the other window (let's call this Window B), click "Home Folder"
 9. Open the "Documents" folder
10. From Window A, drag "New" folder onto Window B ("Documents")
11. In Window B, drag "New" folder back onto Window B ("Home Folder")

At no point was there any freezing or even really reduced performance.

This was in a virtual machine, so maybe that's part of the problem, but I think it's more likely that the issue is that clear steps to reproduce aren't there.