That is because "parentFileNameHint=" in the "Disk DescriptorFile" of the Linked Clone .vmdk file is using the fully qualified pathname to its parent disk and if you move the Parent VM then the "parentFileNameHint=" in Linked Clone's .vmdk file needs to be edited to reflect the change in location of the Parent VM.
If the virtual hard disk is a "twoGbMaxExtentSparse" type disk this can be easily edited as the base .vmdk file is just a text file however if the virtual hard disk is a "monolithicSparse" type disk then the "Disk DescriptorFile" has to be extracted, modified and infected back and this requires third party utilities. In either case backup appropriately before editing the .vmdk file.