Clicking on cows with buckets completely removes the bucket from the inventory and doesn't return a milk bucket

I was playing survival and wanted to craft a cake in 12w17a,
so I walked up to a cow with my 3 buckets (unstacked),
clicked the cow 3 times and the buckets were completely gone from the world without giving me 3 buckets of milk back.

I expected a milk bucket for every bucket I used on a cow!

1. Find a cow
2. Use a bucket on the cow
3. Output: 0 buckets of milk, 0 empty buckets