This is broken very badly in Yosemite. It has to be done via command-line when it is more reliable but requires two steps. Since you a 3TB disk, and Bootcamp needs to be at the beginning of the 3TB disk, if you are willing to try the following in sequence, it may work. Please ensure that you have a full backup of your OSX installation. Since I cannot cut/paste from a screen image, please substitute full values as you need for <placeholder> tokens where I have entered the first few characters of UUID strings.
1. The 3TB disk needs to be split into three parts.
part0 = OSX, 1000gb (this is currently your entire disk1s2 partition). This is being reduced to 1000GB.
part1 = Bootcamp, size
part2 = OSX Remainder (size will be = 3TB - (1000gb + Windows Size))
Use diskutil cs resizeStack to reduce the 3TB disk into two chunks. The first chunk/partition will be your BOOTCAMP partition.
diskutil cs resizeStack <2DC8733C-AE68-...> <A2F14533-FE16-...> 1000g fat32 BOOTCAMP <WindowsSize>g jhfs+ <part2Name> <part2Size>
2. part2 needs to be merged back into the CS volume. The disk slice will be numbered disk1sN. You can find the 'N' by running diskutil list command. Most likely, it will be numbered disk1s5.
diskutil cs addDisk <22B5331F-37A7-...> <disk1sN>
Here are the 'man' pages for the two commands.
diskutil cs resizeStack
Usage: diskutil coreStorage resizeStack
lvUUID|MountPoint|DiskIdentifier|DeviceNode [pvUUID] size
[part1Format part1Name part1Size part2Format part2Name part2Size
part3Format part3Name part3Size ...]
Resize both a logical volume and one of its underlying physical volumes in a
single operation. A single physical volume is always chosen for the underlying
shrink or grow, even if the logical volume's logical volume group is backed by
more than one physical volume. If you do not specify a particular physical
volume, then one is chosen for you. Note that if this is a grow operation,
this verb is limited by the physical volume's partition's room to grow.
Specifying zero as the size asks for an "automatic" grow-to-fill operation.
If this is a shrink operation, you can optionally request that new partitions
be created in the newly-formed free space gap in the partition map.
Again, note that this only resizes one of the underlying physical volumes; if
you need more sophistication in managing your topology, you should use the
separate physical and logical volume resize verbs.
Example: diskutil coreStorage resizeStack
11111111-2222-3333-4444-555555555555 10g JHFS+ New 1g
diskutil cs addDisk
Usage: diskutil coreStorage addDisk lvgUUID NewMemberDeviceName
Add a new physical volume to a CoreStorage logical volume group.
Ownership of the affected disks is required.
Example: diskutil coreStorage addDisk
11111111-2222-3333-4444-555555555555 disk4s2
