19.352 style:text-align-source states that "If the value is value-type, the text alignment depends on the value-type of the cell." It fails to state what the dependency is.
Gnumeric has a default alignment that aligns text "left" and everything else "right".
OOo appears to do the same with perhaps "right" replaced with "end" and "lelft" with "start".
I suspect that this is intended here.