IsLocal=False does work. Never had any issues with it in 5 years. Possibly you have an old version of the Action cached in the Rules. Remove the Serial Update from the Rules, save the Rules, add the Actions back in, and Save the Rules.
V4 way a long time ago 
and much has changed. I suppose it is possible that some optimization is creating a race-condition and the update is not occurring fast enough before the Ticket is Tagged.
##Try this:
Another way to increment a value (and the way I always do it), is like this:
