Linespread "one and a half"

[NicoWinger]

Hello,
 
I'm writing my thesis and recognized that the settings for linespread "one
and a half" (german: "eineinhalb") in document-->settings-->textformat don't
conform to the linespread 1.5 but to the linespread 1.25!!! Can s.o. explain
that? It's really dangerous if s.o. notices that not until he has already
written his maximum number of pages.
 
best regards
 
Nico