The beginning - look my topic Virtuemart 2 Development and bug reports »Search not work February 25, 2012)
As a result of experiment it was found out that the standard module of search Joomla 2.5.1
Has no problems with search phrases of type 12345-654321 though similar uses thus VM search plagin
(http://s017.radikal.ru/i442/1202/60/cf9d27173e08.jpg)