I concur with Sean McConnell. Try to clear the space above the resource being collected before mining the items. It seems to be the only way to prevent losing items to this bug. Unfortunately, this method will also use more of the tool's durability, but it is worth it to not lose items IMO.
Also, try to be patient with Mojang on this issue. I'm sure they are working on it or will very soon if not already. They have a lot on their table due to other Snapshot bugs. Remember, this is a Snapshot, not a final release.
I can confirm this as well. I was mining at level 10 and only one of two lapis ores I silk touched showed up in my inventory. Found it at level 70 right above where I was mining.
I concur with Sean McConnell. Try to clear the space above the resource being collected before mining the items. It seems to be the only way to prevent losing items to this bug. Unfortunately, this method will also use more of the tool's durability, but it is worth it to not lose items IMO.
Also, try to be patient with Mojang on this issue. I'm sure they are working on it or will very soon if not already. They have a lot on their table due to other Snapshot bugs. Remember, this is a Snapshot, not a final release.