SDL 1.3 Timers

This is a duplicate of a query posted on the SDL Development forum but
didn’t make it through to the newsgroup:

Could someone please instruct me regarding differences in timers between SDL
1.2 and 1.3?

I’m trying to get timer code that is running with SDL 1.2 to run with 1.3. I
am initializing the timer subsubsystem. SDL_WasInit says it is initialized.
I use SDL_AddTimer to create a 50 msec timer, and it returns a non-zero
timerID. However, the timer never fires. At least the timer event handler
identified in the second parameter of SDL_AddTimer never gets called.

Is there a test case that includes a timer? I’ve looked without success.
Short of that, perhaps some diagnosis suggestions.