selecting a font into two DCs

I created a DIB using CreateDIBSection, but when I wrote on it using GDI functions, I noticed
that windows didn't perform any anti-aliasing like it did when I created a DDB. (I'm using Windows 98, but
I'm not sure if that makes any difference). But, I accidentally selected my font into two DCs, first one corresponding
to the screen, then into the memory device context that the DIB was selected into. And, lo and behold, the output
was anti-aliased. Does anyone know why?