CALCFIELDS clears blob

Why is that, when i run calcfields on a blobfield it is instantly cleared.

I load a text file into a blob, and it's there, but when i call CALCFIELDS it gets emptied

also when i try to transfer the BLOB value to other table by: "Mytable.blob := TempBlob.blob" it is there before the insert, but after i read the blob from mytable again it is empty