Strange behaviour while assigning date to task

["G. Martin Butz" <mb@mkblog.org>]

Hello,

since I upgraded to Emacs 24 (24.3.50) using org (8.0.7) I sometimes 
encounter a strange behaviour while assigning or reassignig a date to a 
task. The calendar buffer is being displayed at least in two windows; 
the agenda window disappeards and when trying to choose a date Emacs 
says e.g.: No window up from selected window. When I hit enter the 
debugger says:

Debugger entered--Lisp error: (wrong-type-argument integer-or-marker-p nil)
   org-agenda-switch-to()
   call-interactively(org-agenda-switch-to nil nil)
   command-execute(org-agenda-switch-to)

See a screenshot here to illustrate, what I see: 
<http://www.mkblog.org/download/emacs-org-mode-calendar.png>

I can not reliably reproduce this behaviour, sometimes it happens, 
sometimes not. Usually I have to restart Emacs in order to get the date 
assignment to work at all.

Any tipps how I could find out, what this behaviour is about?

Thanks
Martin

-- 
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| G. Martin Butz, mb@mkblog.org, 0421 98749324, www.mkblog.org |
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