I went to load a world up using the vanilla snapshot server, and I found whenever I threw items out of my inventory using Q, they were invisible. They did not disappear after a few seconds, they disappeared instantly. A friend of mine complained of the same problem, and he's running Windows 7 with Java that is up to date.
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I have the same issue in survival SP, have not tested creative, but it's only items that are not blocks that are invisible. Cobblestone, iron, etc. are visible. Tools, redstone dust, diamonds, coal are not. Was able to see the top edge of the coal after it has moved because a block has been placed at it's previous position. Can't confirm the position update was in cause, though, as I was unable to replicate it (but have not tried for long, either).
I am having the same problem in the most recent snapshot. I am in Creative mode and discovered last night that using water to harvest wheat makes the wheat sprites disappear. Today I noticed that throwing things with Q is causing the same thing to happen. I know that technically the items are still there because if I walk around I hear the pickup sound. I should also mention I am running it on OSX Mavericks.