I haven't been able to reproduce this in my test environment. When you do see this happen, can you please take a screenshot?
Sorry for the delay. While using Producteev today I was able to reproduce the error and get a screenshot. I was adding a tag and then added a comment. When posting the comment is when the error happened. If you leave the page where you had the task, it's forever gone and isn't in producteev at all. Hopefully this will help!