I was trying to copy and paste from
https://en.wikipedia.org/w/index.php?title=Meringandan&oldid=925489346
Specifically the 2nd sentence in the lede para, "At the 2011 census, Meringandan ..." including its citation.
OK, I opened it in the Visual Editor, selected and copied it.
I then went to paste it using the Visual Editor into the then current version of that article into the History section. No citation was copied. I thought I must have not selected the citation when I copied. So I went back and repeated the copy making sure that I had dragged across to include the citation. Note that in the Visual Editor the selection of a citation at the end of the sentence is not visually highlighted so missing it can easily happen (aside, could this please be fixed!). Again, the paste failed to bring across the citation. I tried pasting into my user page (in case it was a problem due to being a different version of the same article). Still no citation.
FYI The wikitext was
At the [[Census in Australia#2011|2011 census]], Meringandan had a population of 305.<ref name="census11"/>
I went back and this time selected the sentence and the citation right through to the following heading so there could be no question that I had selected the citation. Again, no citation was pasted but yes the heading was pasted.
Now I had been doing some similar edits a few minutes earlier without problem. e.g.
https://en.wikipedia.org/w/index.php?title=Atherton,_Queensland&diff=prev&oldid=933499193
https://en.wikipedia.org/w/index.php?title=Brigalow,_Queensland&diff=prev&oldid=933499033
but when I look at the wikitext I was copying it was
At the [[Census in Australia#2011|2011 census]], Atherton had a population of 7,287.<ref name="ABS">{{Census 2011 AUS|id=SSC30065 |name=Atherton (State Suburb) |accessdate=13 February 2015 |quick=on}}</ref>
At the [[Census in Australia#2011|2011 census]], Brigalow and the surrounding area had a population of 404.<ref name="ABS">{{Census 2006 AUS|id=SSC35387|name=Brigalow (Chinchilla Shire) (State Suburb)|accessdate=2009-03-31|quick=on}}</ref>
Spot the difference. These citations were not reuse of another citation. This appears to be the point of difference.
Now I copy article content with citations around all the time in the Visual Editor. I can't imagine that I have never stumbled on this bug before now so I think it must have been introduced recently. I have not been that active on-wiki over the past month due to summer holidays, so maybe over that time frame.