bergie/phpcr-odm — comment on commit ae5c19f50349b35d20a3447345d0c820572f0d64
File: lib/Doctrine/ODM/PHPCR/Document/File.php line 183
By dbu:

i found this in the spec:
http://www.day.com/specs/jcr/2.0/3_Repository_Model.html#3.7.11.8%20mix:lastModified

saying that the field /may/ be automatically handled by the repository. so at least for some implementations, what you try to do would be forbidden.
probably you need to get the node type information for mix:lastModified and check if the lastModified property is protected or not. or we could hardcode it for known repository implementations and just get the node type for unknown implementations, to avoid the overhead.

(sad that they did not decide on one or the other imo)