If I have a replay that always triggers a rare bug is is 'always' able to reproduce? I vaguely recall being told that but would like to confirm or be corrected.

Reproducibility refers to the odds of capturing a bug on tape (demo), at least for simulation code.

"always" == you can create the bug/condition without exception at any point you desire given the same initial setup, every time you run Spring.

"sometimes" == !"always" and !"random" (still implies deterministic factors)

"random" == the bug/condition has as much chance of being created as it does of not showing up at all (implies non-deterministic factors and playing back the tape might be useless) for any run of Spring.

Without further information yours would be "sometimes".

Perhaps a Mantis article on the wiki to explain such etiquette?