Wikimedia Bugzilla is closed!

Somebody edited MBTA accessibility
(http://en.wikipedia.org/wiki/MBTA_accessibility) on 05:14, 13 November 2005
68.160.178.62, intending to add "Subway and commuter rail - Reconstruction of
State Street has started", but this resulted in truncation of several
sections/subsections below that.

I found that this is an accident due to a bug: often, if you attempt to edit the
previous revision (02:34, 10 November 2005 134.174.110.5) as the whole article
(and this is the version that user 68.160.178.62 would have been editing from),
the deleted content is already missing in the Edit window. (And the article is
long enough that if you really just wanted to edit something in the middle, you
might easily not notice.)

I had to go to the revision before that (02:33, 10 November 2005 134.174.110.5)
to avoid this problem (although success in avoiding it might be just chance,
since this bug does not occur 100% of the time). Something in the 02:34, 10
November 2005 134.174.110.5 revision causes the editor to mess up, but I can't
think of what it would be, since both that revision and the previous one are
ones that I edited (I was 134.174.110.5), and the only change between them was
to add a note about elevators being out of service.

This seems to be reproducible often, but not 100%:

1.  Go to
http://en.wikipedia.org/w/index.php?title=MBTA_accessibility&action=history (or
get there from the the article by clicking on "history").
2.  Click on revision 05:14, 13 November 2005 (if necessary, page back to get to
it).
3.  Look at this version of the article and note the sections/subsections that
it has (bold text "Massachusetts Bay Transportation Authority accessibility"
before these isn't actually a section heading):
        Subway and commuter rail
        Center island stations
            Blue Line
            Green Line
            Orange Line
4.  Click on Older revision -- you will now be on 02:34, 10 November 2005.
5.  Look at this version of the article and note the sections/subsections that
it has (including spelling errors -- if you see these without the spelling
errors, you aren't looking at the the version upon which I saw this bug occur,
although I can't rule out that it might show up in some other version):
        Subway and commuter rail
        Center island stations
            Blue Line
            Green Line
            Orange Line
            Red Line
        Buses
        Visually Impared
        Hearing Impared
        External links
6.  Click on "edit this page".
7.  Look at the text in the editor window/text box and note the
sections/subsections that it has.

Expected result (which actually occurs some fraction of the time):
*   All of the sections/subsections in revision 02:34, 10 November 2005 will be
present.

Actual result (seems to be most of the time):
*   Only the sections/subsections in revision 05:14, 13 November 2005 are present.

Note:  I set the Version to the latest stable version of MediaWiki noted in the
Wikipedia article about MediaWiki, but I cannot find a way to determine that
this is the version that Wikipedia is actually using as of the time of this bug
report.

I marked this bug as Major Severity and High Priority because it can cause loss
of content without warning, but not Critical Severity and Highest Priority
because I have never run into this bug on any other article (after approximately
a year of use).