Search builder for Pledge recognising > as =

When doing a search with "search builder" for pledges it reads these operators:
>=
>
< or
<=

as =

e.g. a pledge for 300 is found if I use any of the above operators with the value 300. The reult it gives is: "20 Results Amount - = "300""

But if i search for >= 290 it won't find the 300 value and returns the following: "No matches found for: Pledge Amount - = "290" "

It reads all the oprators as =