If a collection happens to pick up a Comment/Discussion Item, it will give the following error when using for example your Thumbnail View:
Module zope.tales.tales, line 696, in evaluate
URL: /var/lib/zope4.3.acpt/buildout-cache/eggs/plone.app.collection-1.0.13-py2.7.egg/plone/app/collection/browser/templates/thumbnail_view.pt
Line 12, Column 0
Expression: <PathExpr standard:u'context/getFoldersAndImages'>
Names:
{'args': (),
'container': <Collection at /clients/xxx/project-area/168-170-blenheim-rd/photos/comments>,
'context': <Collection at /clients/xxx/project-area/168-170-blenheim-rd/photos/comments>,
'default': <object object at 0x1f244e0>,
'here': <Collection at /clients/xxx/project-area/168-170-blenheim-rd/photos/comments>,
'loop': {},
'nothing': None,
'options': {},
'repeat': <Products.PageTemplates.Expressions.SafeMapping object at 0xbde6470>,
'request': <HTTPRequest, URL=http://client1.zope43.acpt.thevirtual.co.nz/clients/DAXGroup/project-area/168-170-blenheim-rd/photos/comments/thumbnail_view>,
'root': <Application at >,
'template': <Products.Five.browser.pagetemplatefile.ViewPageTemplateFile object at 0xa1736d0>,
'traverse_subpath': [],
'user': <PropertiedUser 'robyn'>,
'view': <Products.Five.metaclass.SimpleViewClass from /var/lib/zope4.3.acpt/buildout-cache/eggs/plone.app.collection-1.0.13-py2.7.egg/plone/app/collection/browser/templates/thumbnail_view.pt object at 0xe6f1390>,
'views': <Products.Five.browser.pagetemplatefile.ViewMapper object at 0x7f6975966490>}
Module zope.tales.expressions, line 217, in __call__
Module Products.PageTemplates.Expressions, line 155, in _eval
Module Products.PageTemplates.Expressions, line 117, in render
Module plone.app.collection.collection, line 191, in getFoldersAndImages
Module plone.app.contentlisting.catalog, line 44, in __getattr__
AttributeError: isPrincipiaFolderish
We found this when creating a collection by tag, as it will pick up any comments on the tagged objects as well.