Actionscript 3 :: Memory Leak In Server Polling Presentation App?

I'm building a remote presentation tool in AS3. In a nutshell, one user (the presenter) has access to a "table of contents" HTML page with links for each slide in the presentation, and an arbitrary number of viewers can watch the presentation on another page, which in turn is in the form of a SWF that polls the server every second to ensure that it's on the right slide. Whenever the admin clicks a slide link in the TOC, the database gets updated, and on its next request the presentation swf compares the label of the slide it's currently displaying to the response it got from the server. If the response differs from the current label, the swf scrubs through the timeline until it finds the right frame label; otherwise, it does nothing and waits for the next poll result (a second later).

Each slide consists of a movieclip with its own nested timeline that loops as long as the slide is displayed. There's no actionscript controlling any of the nested movieclips, nor is there any actionscript on the main timeline except the stop();s on each keyframe (each of which is a slide in the presentation).

Everything is built and working perfectly. The only thing that's troubling is that if the presentation swf is open for long enough (say, 20 minutes), the polling starts to have a noticeable effect on the framerate of the movieclips animating on any given slide. That is, every second, there's a noticeable drop in the framerate of the animations that lasts about three-tenths of a second, which is quite noticeable (and hence is a deal-breaker for the whole presentation suite!).

I know that AS3 has issues with memory management, and I've tried to be diligent in my re-use of objects and event listeners. The code itself is dead simple; there's a Timer instance that fires every second, which triggers a new URLRequest to be loaded by a URLLoader. The URLLoader is reused from call to call, while the URLRequest is not (it needs to be initialized with a new cache-killing value each time, retrieved from a call to new Date().time). The only objects instantiated in the entire class are the Timer, the URLLoader, the various URLRequests (which should be garbage-collected), and the only event listeners are on the Timer (added once), the URLLoader (added once), and on the routines that scrub backwards and forwards in the timeline to find the right slide (and they're removed once the correct slide is found).

I've been using mr doob's stats package to monitor memory usage, which definitely grows over time, so there's gotta be a leak somewhere (it grows from ~30 MB initially to > 200 MB after some scrubbing and about 25 minutes of uptime).