Thanks for the hint, the overwriting of an css rule which is used moodle wide was the cause of this behaviour. It is fixed now with the new build .
General help
Can't resize text area
ការពិភាក្សាត្រូវបានបិទ ដូច្នេះអ្នកមិនអាចឆ្លើយតបទៀតទេ។