Additional detail is pretty hard to come by. Identifying click and drag as a causative factor is a revelation, and generally is the limit of the Blogger's observation.
Today we have a well written and conducted case study, documenting one instance of the problem.
Possibly relevant details:
- What operating system and browser (name and version please) do you use?
- Did you clear cache before trying your test?
- What add-ons do you have in your browser, and which ones were active when you were doing this?
(Update 6/8): Blogger tells us that there is a known problem with using Internet Explorer V6 and Compose mode to move photos. If you're using IE V6, move photos in Edit HTML mode. Cut and Paste - don't Drag and Drop. Or upgrade to IE V7, or switch to Firefox.
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