I have had a gate on the block under the cross-hairs in the picture, and occasionally it disappears. It is no longer there, and I have placed another gate, only to have it happen again and again. Sometimes it takes a while for it to happen, and I might have traveled far away for a while in the mean time.

<edit> This seems to be the only gate that keeps disappearing. I have other gates up at ground level, and they are still there. The coordinates for this one are -9, 11, 7.

I saw there WAS a problem with this before, but it was marked as resolved. Doesn't seem to be resolved though.