I had a workflow that, no matter what I changed, when I published it, it looked like it published successfully, but it actually didn't. I came across this link that mentioned copying an email can cause problems. The problem stems from SharePoint designer trying to copy the variables in the email. It just can't handle it.
The beauty of copying an action is to avoid having to paste in all the workflow variables in a highly formatted email. If it can't handle the variables, then this is pretty much useless. I ended up deleting the emails I copied and re-creating each one by scratch and then it worked fine ( I didn't want to lose all the other work I had already put into the workflow by starting over).
I suspect the problem would occur with any action involving variables you try and copy, so just stay away from the copy function. The link above mentioned that this is only an issue with tasks, but it's not worth figuring when it does or doesn't work.