[plt-scheme] compiling flickr.plt via PLaneT doesn't create a "compiled" directory

I have a trivial program that uses flickr.plt (attached
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); whenever I run it on a particular box, it takes a _long_ time to
run.  I suspect it's compiling itself every time I run it (instead of
what I would expect, which is: it compiles itself just the _first_
time I run it, and thenceforth it's fast, since it can load the
already-compiled code).

Now, the problem only happens on my *nix box, which is running a
not-too-old build of mzscheme (371.2, which I built myself) -- but on
Windows, using a pre-release labeled 371.3, it works fine: it was slow
the first time, but took only a second or two the second and
subsequent times.

I also note that on the troublesome *nix box, I do not have a
directory named
~/.plt-scheme/planet/300/371.3/cache/dvanhorn/flickr.plt/1/0/compiled
whereas on Windows, I do have the equivalent directory.

So my guess is that somehow the compilation process is failing
silently.  How can I debug this?
-- 
When a cryptographer and a symbologist get together, it
usually ends in tears.
        A. O. Scott, reviewing 'The Da Vinci Code' in the New York Times