SL & partition resize - Why not one only?

Hello at all.
I need to enlarge partition of my Time Machine

I have an external 1TB hd, based on GUID map scheme, split into 2 partition:
1st 600GB hfs+ journled (with my TM) - partion A
2nd 400GB ntfs (data) - partition B

By disk utility, I tried to remove the 2nd, but when do that, the alert says me that "partition A will be deleted", "partition B will be deleted".
Why?
It depends by ntfs format on 2nd?
If I initialize the 2nd partition (400GB) into hfs+, and successively try to delete it, I'll have the same alert type?

Thanks
Dario

I tested for Partition A too;
so I select partion A, type "-" sign, result is the same;
system always response alerting about, both partition will be deleted, even if I select only one of them.

...and...
using linux "Gparted" to remove the B Partition, could create problem?

..any idea.
Someone know a tread where this type of problem is mentioned?