Restoring default cache settings after node restart

Hey folks,
I've been playing around with cache settings recently, mainly related to
the field cache, and I've been unable to figure out how to restore the
defaults (e.g. unlimited). The docs seem to indicate that I should be able
to set both index.cache.field.max_size and index.cache.field.expire to -1
to get the defaults. This works until I restart the node at which point I
get an exception about "maximum size must not be negative" or a similar one
for the expiration time and the index won't load.

The workaround seems to be to set both values to something other than -1
(say 1 and 5m) at which point the index will load and then you can set them
back to -1 again. Obviously you'll have the same problem next time you
restart.

Am I using the wrong values here? If so, should there be some validation
when the values are set in addition to when the index is loaded after a
restart?

Thanks,
-Tim