Thaumcraft 4.2.3.4
Carpenter's Blocks 3.3.5

Place a Carpenters Block and "fill" it with a Diamond Block.
If you "break" it with the excavation focus you get 2 Diamond Blocks and the Carpenters Block back.

Posted this to Azanors Git too

I guess I forgot to mention, I addressed drops in 3.3.7 DEV some time ago. Specifically it was intended to fix this issue, but in the process made the drop system more robust overall.

Thanks for the report. Block drops are tricky to get right, and I assumed the last fix for Buildcraft seemed pretty solid. Though, torches and levers also had a different way of dropping that needed to be corrected. We'll see what Azanor says.