Are you sure? I also use LaTex in my blog but I've not found such an error. I don't know whether forums support LaTex or not. But let of try: I wrote $latex \displaystyle {\sum_{i=0}^{\infty}} f_i(x)&s=2$ by using

$ l a t e x \ d i s p l a y s t y l e { \ s u m _ { i = 0 } ^ { \ i n f t y } } f _ i ( x ) & s = 2 $.

And again I wrote:

$latex \displaystyle {\sum_{i=0}^{\infty}} f_i(x)&s=2$ by using $ l a t e x \ d i s p l a y s t y l e { \ s u m _ { i = 0 } ^ { \ i n f t y } } f _ i ( x ) & a m p ; s = 2 $

Both rendered the same on my blog draft.