TYPO3 Core

For content elements the select box "Transl.Orig" modifies the l18n_parent field. The wizard (and the button to activate it) to translate content elements looks for elements using the l10n_source field.
This works fine if translations are made, but when someone edits an element in a non-default language and changes the l18n_parent field things start to go wrong.

Example with English as default language and German as translation.
1. Create an English element "en1"
2. Create an English element "en2"
2. Create a German element "de1"
The page indicates "free mode" for translation.

3. Edit the German element "de1" and set "en1" as the 'Transl.Orig' value. This modifies the l18n_parent field.
The page now indicates "connected mode".

4. Use the "Translate" button to translate the English content to German.
Now two (!) content elements have been added to the German page, translations of "en1" and "en2".