The reason I am listing this as a bug is because this behavior from Lightroom serves no rational purpose and negatively impacts the general user population.
1. Import "x" number of photos. "x" in bytes being larger than the available amount on the local storage.
2. Lightroom 5.3 first and wrongly copies the photos from the SD card, to the "Local Storage" "Storage location for origionals" directory. Usually /Users/name/Pictures/Lightroom.lrlibrary.
3. Lightroom 5.3 tries to sync these photos to the user's "Creative Cloud".
4. You run out of hard drive space mid way between syncing these photos to creative cloud and moving them to your "Local Storage" directory.
5. Lightroom won't be able to show you previews of any of the pictures already on the cloud and you won't be able to work on or add any further photos as you're harddrive is 100% full.
Proposed Solution: For the initial import, Instead of SD -> Local Directory -> Cloud
Just do SD -> Cloud
Then after that download and cache the pictures that actually need to be worked on, that's a much smaller size than demanding all photos be stored locally before moving to CC. It really serves no purpose.
This is as designed. If Lightroom would do SD > Cloud directly, then importing images would not only be very slow (depending on your network speed), but there would also be a risk of losing images because of connection errors.