Don't think that's correct. The "Build My Kubota" app on the Kubota website lists 4 different bucket options for the Grand L's: 1) Light Material, 2( Standard Square Back, 3( Heavy Duty Round Back, and 4( 4 in 1. I've been using the standard square bucket for 14 years of serious use (ex: digging piles of 10-12" rip-rap, carrying logs up to 2,000lbs using pin-on forks, moving Lord knows how much material, etc.), with no warps, cracks or bends of any kind. Seriously, unless you expect to do something really extreme, the standard bucket is plenty rugged. Here's a pic of the standard bucket on mine.
Here are LA805 bucket specs from the Kubota Canada website, where both square and round back buckets are called "standard":
Standard bucket
Width 72 in. (1830 mm)
Type Quick attach
Depth Round 72'' 18.0 in. (458 mm) Square 72'' 547mm (21.5 in)
Overall height Round 72'' 23.9 in. (608 mm) Square 72'' 570mm (22.4 in)
Length Round 72'' 24 in. (610 mm) Square 72'' 630mm (24.8 in)
Standard
Capacity - struck 10.9 cu. ft. (0.31 mウ)
Capacity - heaped 13.1 cu. ft. (0.37 mウ)
Standard bucket
Weight Round 72'': 397 lbs. (180 kg) Square 331 lbs. (150 kg)
Can't swear to it but some checking seems to suggest the Kubota "Light Material" bucket is a snow bucket. Here's a link with a photo of one:
http://www.tractorbynet.com/forums/attachments/268362-kubota-light-materials-bucket-too.html
Any decent dealer should have all the details about this.
Hope this is helpful.