The T3 uses the enhanced PIM applications and since you didn't specify which Zire you use then here's my 2C on what I'd do....go buy Chapura's Pocket Mirror XT. It should work with the T5 because the conduits are essentially the same.
You can then better address the situation through the XT's options settings.
Also, are you using any other PIM application on the handheld besides the core Palm PIM's such as Agendus or Datebk? the T5 is causing some havoc here with both of those programs because of changes to the file structure. Both apps will probably be updated but I'm much more comfortable in using Pocket Mirror XT with the T3 because of the Outlook sync issues.