TYPO3 Core

Try this:
build a short form with one select field.
use for one option a label with a . (dot) in it e.g. test.test. Copy this in the value field too.
Save the form. Everything is correct, the yaml file is correct and the output in the frontend too.
Close the form modul in the backend and reopen it. Activate the select field:
- the option is vanished
- in the widget for the options you see: [object Object] and in Value test.
Save the form once again. The yaml file now contains errors:
options:
test:
test: test.test
and the front throws this error:

Uncaught TYPO3 Exception
#1476107295: PHP Warning: get_class() expects parameter 1 to be object, array given in /Volumes/web/src/typo3_src-8.7.4/typo3/sysext/fluid/Classes/ViewHelpers/Form/SelectViewHelper.php line 231 (More information)

TYPO3\CMS\Core\Error\Exception thrown in file
/Volumes/web/src/typo3_src-8.7.4/typo3/sysext/core/Classes/Error/ErrorHandler.php in line 112.

the dot is necessairy for dates or many other special labels. It seems that the error occurs when the form wizard reads the yaml file.