TYPO3 Core

• TYPO3 11.5.19
• mask 8.0.5 (According to nhorvatov, this is a TYPO3 issue, even if it was discovered when using mask!!!)
• PHP 8.0

1. Install mask 8.0.5
2. Create a repeating mask element, let's name it "Categories".
3. Create a repeating element within "Categories", name it "Subcategories".
4. Create an RTE field within Subcategories, let's name it "Description".
5. Go to a page and add the created content element
6. Add 4-5 Subcategories with complete descriptions (Test 1 until Test 5) and save the content element
7. Open the content element again and create a new subcategory below the previous created subcategories and move it's location up 4 positions (with the arrows which change the sorting).
8. With each position the new subcategory has moved up, the field "Description" has been duplicated (multiple fields among themselves)

Result: