Question of Update item in a Loop

[#1]

I met a problem when i run a loop. 

I have a form with two columns named "content" and "comment", when user write something in the comment, the workflow will append the comment to the end of content.

So I make a workflow to start a loop. In the loop I do:

1.Wait for item update (wait for comment is not null)

2.Build string (concentrate content and comment and store in a variable)

3.Update item (write variable to the content column)

4.Update item (clear comment column)

5.Commit pending changes

When the loop run the first time it is OK. I write something in the "comment" and it is append to the "content" successfully and the comment is cleared.

When I write something to the comment again, the workflow stop at the "Loop" action, after about 5 minutes, the second loop seems start to run. But it append the same comment twice to the content.

I'd like to ask why the loop not start immediately, and why the action be done twice in one time loop .

Please help me see the question. Thank you.

[cassymfreeman]

can you post your workflow?

one question though - why not just have a workflow with a simple update item action in it which runs conditionally on item update where comment has changed?

[#3]

Dear Cassy,

Thank you for helping. The Workflow is as follows.

I found "Start when items are modified" in the settings, is that the function? I think this is the right way. I made it complicated.

Yet I am still curious to know the detail of loop interval. Would you please see it if you have time. Thank you.

[cassymfreeman]

how were you initiating this workflow?  What action is "Get Comment" above?

[praios81]

Are you using plain text fields for your scenario or do you use the "append text" option for the content's column? If you use append text all the old comments will also remain in your feed.

Couldn't you just use the append text option without any workflow instead?