I have a SharePoint workflow, developed with SharePoint Designer, which is supposed to compare values in the list it is attached to against values in another list, and copy the other list’s values if they are different. I kept noticing, via a workflow history log message, that the workflow was copying values every time it ran, even though in another log message for the same workflow instance it showed me that all the values were the same.
As it turned out, I was comparing a string value to a list ID. Even though they both printed in the log message exactly the same (and so were “equal” in my eyes), SharePoint saw them as different values.
The fix was to copy the list ID value to a string variable, and then compare the two values as strings.
[As a side note, what made this worse was that I had a second workflow which would run when anything was changed on the list. It would then update a value in the list, which would then cause the buggy workflow described above to run again. For the astute readers, this meant that the two workflows attached to the same list would cause each other to run infinitely. It pretty much brought the site to a halt!]