[Zope] Asked for authentication when reading property after upgrade from 2.6 to 2.7

[Uli Franke]

This problem occurs in a project that works perfectly with ZOPE 2.6. 
After the upgrade to ZOPE 2.7.4 the user is asked for permission when 
ZClass code references a property defined in a property sheet.

More detailed: A tal command of a ZPT inside a ZClass tries to access a 
property that is defined in a property sheet of the same ZClass, but is 
- of course - given a value in the instance of the class. In ZOPE 2.7.4 
the user is asked to authenticate, and if he cancels authentication he 
gets the message:

"Error > Value: You are not allowed to access 'teillisten_laenge' in 
this context".

where teillisten_laenge is the property in question. This is just one 
example - the problem seems to occur in all similar cases.

Here's the code fragment that tries to read the value of teillisten_laenge:

   <span tal:define="listen_laenge 
here/propertysheets/listenstil/teillisten_laenge">
     <span tal:define="sort_kriterium string:id">
       ...
     </span>
   </span>

Someone confronted with the same problem? Seems to be a bug, or could it 
be wanted behaviour? Any proposals for a workaround?

Thanks,
Uli