I have increased max_packet_size in MySQL and reuploaded every photo. I
don't see this problem anymore.
I wonder why it's possible to attach oversized photo (>1Mb), but
impossible to delete it (when recycle bin is enabled). I have a
hypotesis that there is a write-back cache.
This cache makes it possible to upload 3.5Mb photo, but it fails to
write it into a permanent store because of MySQL restriction.
Eventually, write-cached item becomes inaccessible.
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