The subject behavior can occur if you have deleted a logical drive from an extended partition, and have NOT removed the extended partition.
To workaround this behavior:
1. Select the last unpartitioned space on the drive and C to create a partition.
2. Select the new partition that you created in step 1 and press D to delete it.
3. If more than one extra unpartitioned space exists on the drive, repeat steps 1 and 2 until the unpartitioned space is combined into a single segment.