typo3 flexform options show invalid values in backend - typo3

Question

I have created a FlexForm for my typo3 backend to choose some options:
<?xml version="1.0" encoding="utf-8" standalone="yes" ?>
<T3DataStructure>
<sheets>
<sDEF>
<ROOT>
<TCEforms>
<sheetTitle>
</sheetTitle>
</TCEforms>
<el>
<settings.maxNumber>
<TCEforms>
...
<settings.orderBy>
<TCEforms>
<label>My selections</label>
<config>
<type>select</type>
<renderType>selectSingle</renderType>
<items>
<numIndex index="0">
<numIndex index="0">Title first</numIndex>
<numIndex index="1">title,year,author</numIndex>
</numIndex>
<numIndex index="1">
<numIndex index="0">Year first</numIndex>
<numIndex index="1">year,title,author</numIndex>
</numIndex>
<numIndex index="2">
<numIndex index="0">Author first</numIndex>
<numIndex index="1">author,year,title</numIndex>
</numIndex>
</items>
</config>
</TCEforms>
</settings.orderBy>
<!-- end of settings -->
</el>
</ROOT>
</sDEF>
</sheets>
</T3DataStructure>
My problem is that the first entries in the dropdown menu in the backend are
1. [INVALID VALUE ("author")][author]
2. [INVALID VALUE ("title")][title]
3. [INVALID VALUE ("year")][year]
then the other options follow as expected.

Answer 1

Documentation about "items" array in "select" type about the second value says:
Values must not contain “,” (comma) and “|” (vertical bar). If you want to use “authMode” you should also refrain from using “:” (colon).
https://docs.typo3.org/m/typo3/reference-tca/9.5/en-us/ColumnsConfig/Type/Select.html#items
It means you should probably use a different separator for those values to avoid the issue you're facing.