The developers don't know why you're getting this error. So they're really glad you contacted them. They added better logging for the cache function in 1.3.2 so that they can figure out why this is happening.
Can you set your debug log level to 10 and reproduce the error? Then please send us the logs so we can go through them. We'd also like to know how many CPUs your server has and what OS it's running.
As the developers say, "If we can reproduce, this should be great"