[TYPO3-commerce] fatal error after editing article prices

[Vajk Zelles]

Hello List, 

at the moment I am facing following problem in a typo3 4.4 / commerce 0.12.4 installation:

when I save after editing / changing / adding a price to an article, with my first attempt I get the following fatal error:
"Cannot use string offset as an array in /path/to/my/installation//typo3_src-4.4.4/t3lib/class.t3lib_flexformtools.php on line 271"
without the actions getting saved.

With the second attempt it normally works, returning "just" a blank frame in BE, reloading the page reveals that all changes are committed.

does anyone have an idea, what could affect this behaviour?

Thanks a lot in advance,

Vajk