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When installing openSUSE Leap 42.3, on a drive that already has an OS (not sure
if this matters, but just putting it out there)

During the installation, click on "create partition setup". When given the
choice between expert or the single drive in the computer, choose the singular
drive.
At the next page, click on "use entire disk" and then click on "edit". in edit
change it from "partition" to "LVM" and uncheck the box for using a separate FS
for the home directory (which by default is XFS while the base FS is BTRFS)

If doing the above then it will create a single BTRFS LVM partition that only
uses 40GB of the drive. tested on both an 80GB and 320GB drive, both cases only
had a 40GB partition and the rest was unallocated.

If you leave it on "partition" instead of LVM then it will use the whole drive.
If you leave in the separate home partition then it will also use the whole
drive.

Reproducible: Always

Steps to Reproduce:
During the installation, click on "create partition setup". When given the
choice between expert or the single drive in the computer, choose the singular
drive.
At the next page, click on "use entire disk" and then click on "edit". in edit
change it from "partition" to "LVM" and uncheck the box for using a separate FS
for the home directory (which by default is XFS while the base FS is BTRFS)
Actual Results:  
40GB of the drive is used, rest is unallocated

Expected Results:  
Entire HDD/SSD is used.