problem with forecast

[serpentes]

hi there,

i have a strange problem with forecast items.
I am trying to do a forecast for disk usages on my monitored hosts. I have working items with the free space which are of the type Numeric (unsigned)
The problem occurs - or gets visible when the free space is above 1TB

When I create a calculated item with the formula

last(//ITEMKEY)

it reads the korrekt value in Bytes - just to check if the item's value is correct - e.g. 1757956354048

when i change the forumula to

forecast(//ITEMKEY,1h,1h)

and klick on "Test" and "Get Value and Test" it reads a wrong value from the key: 999999999999.999878 - which results in 931.46GB
Seems linke forecast reading a float value although its unsigned :-/

can anybody help me pointing this out?