$modx->getParentIds() doesn't work in TV value

This code works fine in front-end, but doesn’t work in manager in TV value. How could it be?

getParentIds() operates only on the current Context as it depends on the Context cache file. There is a feature request to improve this and allow access across contexts, but it is not currently possible.

Had a similar problem yesterday and got some pointers that helped solve it. Here’s the thread:
http://modxcms.com/forums/index.php/topic,66469.0.html

Essentially when a document is loaded in the manager not all placeholders and variables get set. So calls that work fine in the front end will not work in the backend.

I had to write a separate snippet that was called from TV using @EVAL binding.

Hope this helps.