Cannot disallow deletion of nodes and content not updating

This might sound strange. I am having a problem with some roles but not others, even if the Access Control and Taxonomy Access settings are identical. There are 2 symptoms:

1.) Deletion cannot be disallowed. Even if I go into taxonomy access and select deny deletion for every category the delete button still appears.

2.) Most of the time when editing a node, when the submit button is clicked the content is unchanged. This happens approximately 4 out of 5 times!

I'm guessing there must be some corruption in the database but I am not sure where. I have checked that revisions exist for all nodes and that users exist for all nodes. Help would be greatly appreciated!