Good point! In Germany, the dot is a thousands separator, and Kagi (just do the maths) actually seems to interpret "4.619" as "4619". Of course, it no longer does that with two decimal places.
The interesting question, however, is what should be done here. It's not too illogical to assume that Germans calculate with commas (so here "4,619"), it would be a disadvantage in terms of usability, in my opinion, if Kagi were to force English number input. So, in the preview, this is more of a bug...