TYPO3 Core

After adding two flexform items to a record, and selecting all 3 checkboxes on the bottom item, and saving the form the flexform data of the record gets corrupted. The record is then no longer accesible through the typo3 backend, and the only way to fix it is manually editing the record from the database with phpmyadmin, or deleting the record.

I first noticed this bug in the slideshow extension, but it looks like it can be trigged by all extensions which uses this kind of flexforms.

I have made a test exteion to reproduce the effect.

1. Install the test_flexform extension.
2. Add a new "flexform items" record to a sysfolder.
3. Select NEW "flexform item" and save the form.
4. Select NEW "flexform item" again and save the form again.
5. Select all 3 checkboxes beside the bottom flexform item (the delete, move up, and move down icons), and save the form.

After saving the form the flexform data in the record becomes corrupted, and PHP produces the following error:

PHP Fatal error: Cannot use string offset as an array in <sitedirectory>/typo3_src-4.1.5/t3lib/class.t3lib_transferdata.php on line 625

After following the previous steps, the flexform data in the record contains an empty element, which typo3 can't handle correctly:

<T3FlexForms>
<data>
<sheet index="sDEF">
<language index="lDEF">
<field index="fields">
<el index="el">
<section index="1"></section>
<section index="2">
<itemType index="item">
<el>
<field index="item">
<value index="vDEF"></value>
</field>
</el>
</itemType>
</section>
</el>
</field>
</language>
</sheet>
</data>
</T3FlexForms>

The steps I have written down are not the only way to reproduce this bug, other combinations of adding / deleting / moving items will sometimes cause it too.
(issue imported from #M7235)