tcaTree cannot handle records on pid 0 correctly
When using the tcaTree with nested records on pid 0, the parent handling does not work correctly.
The reproduce, you can e.g. allow the table sys_category on the root page by adding
'rootLevel' => -1 to its TCA configuration. Then go to some page (not root), add 3 cats:
bar, set foo as parent
bar 2, set foo as parent
Then add a category to root level, open 'bar' or 'bar 2' again -> parent is not selected anymore.