Changing Partition Sizes

I have a HDD with two partitions, both of which have free space. I wanted to rob some of the free space from partition 2 to make partition 1 bigger but the slider bar reports that the free space available is the existing maximum size of partition 1. If I move the slider bar, the reported size doesn't change.

However, if I try to resize partition 2 using space from partition 1, the slider bar reports that there is oodles of space available. Both partitions are on my second HDD, ie not on the OS drive.

Any clues?

I'm using v10 BTW.

Thanks.

Keith.