PropertyMigrator doesn't properly handle reimporting list values

Reproduction steps:

• Prepare a XAR with following instructions (optional step: a XAR is already attached containing what's needed):

• Create a page XClassTest.WebHome
• Edit it using the class editor and add a static list field named "staticListMultiCustomSep"
• Edit the property to ensure it supports multiselect, it uses input and the separator for edition is "#"
• Create a page XClassTest.MyObj.WebHome
• Create a new object of type "XClassTest" in that page, and provide values "foo", "bar" and "buz"
• Save the page and export the page MyObj only as XAR
• Then delete the hierarchy XClassTest

• Go to Administration > Import
• Import the XAR
• Go to the created page XClassTest.MyObj.WebHome and open the object editor to check the contained objects, it should display a deprecated object with a value "[foo, bar, buz]"
• Without changing anything, go to XClassTest.WebHome and create the page
• Go to the class editor and creates a new static list field named "staticListMultiCustomSep"
• Edit the property to ensure it supports multiselect
• Go back to XClassTest.MyObj.WebHome and open the object editor

Expected result:

• The property value of staticListMultiCustomSep in the object contains "foo", "bar", "buz"

Obtained result:

• The property only contains "foo": "bar" and "buz" are lost