The CommentsTemplate topic includes the UserCommentsTemplate topic using a line like: %TMPL:INCLUDE{"%TWIKIWEB%.UserCommentsTemplate"}%
TMPL:INCLUDE appears to be unable to handle the %TWIKIWEB%, as templates added to UserCommentsTemplate are unavailable. If I replace '%TWIKIWEB%' with simply 'TWiki', templates in UserCommentsTemplate suddenly become available.
Correct. The templates got hacked by someone who didn't test before they checked in. It's fixed in Subversion, and should be fixed in 4.0.2.
Note that the CommentsTemplate topic is changing name to CommentPluginTemplate. It should be seamless for you, but be warned. The change is needed to support users on Windies, which doesn't differentiate case in file names
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