[O] [Bug] Error when clicking in calendar

[Ivan Vanyushkin]

Hello.
There is bug in calendar, that causes error and CUA stops working.

1. Open any .org file.
2. Call calendar (insert date): Ctrl-c .
3. Left-click on any date.

Result:
1. Date is inserted
2. Error is shown in "Messages" buffer:
"Error in post-command-hook: (buffer-read-only *Calendar*)"
3. As effect of error, Ctrl-C stops working correctly: it expects one 
more key even if text is selected.
If I disable CUA mode and enable again, it fixes.

Environments with error:
- Emacs 23.3 and build in org-mode 6.33
- Emacs 23.3 and org-mode 7.5.
- Emacs 23.3 and org-mode from git master branch.

I think, error is related to "(add-hook 'post-command-hook 
'org-read-date-display)" in org.el somehow, but my knowledge is not 
enough to fix it.

Please, help me to fix "Error in post-command-hook: (buffer-read-only 
*Calendar*)".
Thank you.

--
Ivan.