Tools with unbreaking enchantment break, disappear from slot then reappear

What happened:
I was mining to the last of a diamond pick, it broke and I went to replace it with a new one. When I placed the new pick in the slot the old one reappeared and I was able to place it back in my bar. Sometimes I can use the pick, have it break, reappear and be reused several times before it breaks for good. As the pick breaks no breaking sound is heard.

What I expected to happen:
My pickaxe breaks... The end...

How to reproduce:
This seems very intermittent, there seems to be no link to anything. It's not every pick and I haven't noticed it on other items.

/give @p diamond_pickaxe 1 1561 {ench:[{id:34s,lvl:2s}]}

Code analysis: https://bugs.mojang.com/browse/MC-1040?focusedCommentId=288014&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-288014