[OpenStreetMap] #4947: Clicking "Hide areas" on the data panel breaks the slippy map ending up at NaN zoom (was: Clicking "Hide areas" on the data panel breaks the slippy map ending up at NaN coordinates)

[OpenStreetMap]

#4947: Clicking "Hide areas" on the data panel breaks the slippy map ending up at
NaN zoom
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  Reporter:  Deanna Earley  |      Owner:  rails-dev@…
      Type:  defect         |     Status:  new
  Priority:  minor          |  Milestone:
 Component:  website        |    Version:
Resolution:                 |   Keywords:  data nan
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Comment (by Deanna Earley):

 Just tested again with a much simplified:
 1) visit this URL:
 http://www.openstreetmap.org/#map=19/50.91423/-1.33659&layers=D
 2) Press "Hide areas"

 After this, it shows the updated list of objects, but no outlines.
 Attempting to pan changes the scale to sub 1metre/1foot, and the anchor
 text disappears.
 Zooming then "loses" the tiles.
 Panning again then changes the scale to 3000000km/2000000miles.
 Refreshing at this point leaves it at the same scale with still no tiles.

 Looking at the cookies, _osm_location has a value of
 "-180%7C-90%7CNaN%7CMD"

 The page is being rendered in IE9 standards mode.

 This is all reproducable on demand using IE 9.0.8.8112.16421, with update
 KB2846071 (9.0.18) On Windows 7 Service Pack 1.

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Ticket URL: <https://trac.openstreetmap.org/ticket/4947#comment:3>
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