Bug in Paypal plugin, incorrect fee on method selection

[Netflyer]

On our testsystem with Virtuemart Version 2.6.0a the payment fee on the payment selection is not shown correctly. on the checkout screen and on the bill the correct fee is used. the same parameters work fine on the productive system running virtuemart  2.0.24a. the following debug information shows that the plugin at some point does not use the cart value:

vmdebug My selected language by JFactory::getLanguage()->getTag() de-DE
vmdebug $siteLang: de-DE self::$_jpConfig->lang de_de
vmdebug vmTime: loadConfig db no: 0.0155229568481445
vmdebug Start used Ram 9.75M
vmdebug Progressive $cartTotalAmount = (18.9 + 0.55) / (1 - (3.4 * 0.01)) = 20.1345755693582
vmdebug Progressive $cartTotalAmount = 19.45 / 0.966 = 20.1345755693582
vmdebug Part $denominator 17.5 $frac 1 Var1:
1.23457556935818
vmdebug Progressive $cartTotalAmount = (18.9 + ) / (1 - ( * 0.01)) = 18.9
vmdebug Progressive $cartTotalAmount = 18.9 / 1 = 18.9
vmdebug Part $denominator 18.7345755693582 $frac 1 Var1:
0
vmdebug Progressive $cartTotalAmount = (18.9 + ) / (1 - ( * 0.01)) = 18.9
vmdebug Progressive $cartTotalAmount = 18.9 / 1 = 18.9
vmdebug Part $denominator 18.7345755693582 $frac 1 Var1:
0
vmdebug Progressive $cartTotalAmount = (18.9 + 18) / (1 - ( * 0.01)) = 36.9
vmdebug Progressive $cartTotalAmount = 36.9 / 1 = 36.9
vmdebug Progressive $cartTotalAmount = (0 + 0.55) / (1 - (3.4 * 0.01)) = 0.56935817805383
vmdebug Progressive $cartTotalAmount = 0.55 / 0.966 = 0.56935817805383
vmdebug Part $denominator 18.7345755693582 $frac 1 Var1:
0.56935817805383
vmdebug End used Ram 29.5M
vmdebug Peak memory peak 29.75M