This is a longstanding "feature" (as in, "it's not a bug, it's a feature"... for some reason) since ... well i've been here over 10 years now.
There are several reasonable and usable workarounds. All of them involve preventing the user from being able to click on a task's submit button past the expiration timer. My favorite one, of course, is to make the expiration timeout long enough that no user will ever be on the task that long - after all, do you really want to have a user in a situation where they fill out 95% of a form, then wander away to lunch, then come back and everything is lost because the timer fired?
The other main method I usually do, geared more towards forms where a user doesn't actually need to "submit" it in any case, such as a "final confirmation" form, is to present them with a task with NO submit capability - this could include a SafeLink that navigates back to their Site, or just instructions that tell them (for instance) to click on the "Home Tab", etc. These could have a particularly short timeout time value, since the user won't be trying to submit them at all.