TYPO3 Core

Flexform is set by default to this:

<config>
<type>group</type>
<internal_type>file</internal_type>
<allowed>*</allowed>
<max_size>10000</max_size>
<uploadfolder>uploads/tx_tsselect/</uploadfolder>
<size>1</size>
<maxitems>1</maxitems>
<minitems>0</minitems>
<show_thumbs>1</show_thumbs>
</config>

with TSconfig (TCEFORM) i'm changing this values:

TCEFORM.tt_content.pi_flexform.ts_select_pi1.sEXTRA.file.config.size = 6
TCEFORM.tt_content.pi_flexform.ts_select_pi1.sEXTRA.file.config.maxitems = 6

Now the Backend User can select multiple files. But if the user is saving the content element (flexform) any item will be removed only the first leaves (like it's set on the flexform.xml).

So it seems that the TSconfig will change the maxitems value and it looks like it's working but on saving these changes will be ignored and the original flexform.xml config will be used to save the data.