Non-Director authors shouldn't be able to modify their uploaded files after the submission deadline has passed, with one exemption: for a breakdown on how this works, see viewtopic.php?f=3&t=2675&p=9618#p9618
. However, as you've pointed out, this is not the case for presentation metadata, which can be modified at any time. I agree that these fields should also be locked down -- would it make sense to you if the same rules that apply to submission files also applied to the submission metadata? If so, I'll post a bug report.