Using the 1.2 mobile API, I create a new Android project, open up app.js, and add on the bottom line:
No alert dialog appears in the emulator. If I comment out the tabGroup.open() line, I do see the alert. This unfortunately also affects JS debug messages - if the tab group is already open, I never see a message that the JS is buggy.
This problem doesn't seem to occur when building for iPhone.
Use the Ti.API.debug info, warn, error method for now. It's a known bug. Ticket 619