as tomas and, I think, Druidek pointed out, just open hdtoolbox, pick the partition and change the dos type identifier thingie to something else, for instance just random values, exit, save changes, click yes, when it says it will destroy your partition, and off you go, no more invalidations
Of course you need to change it back to ffs or whatever filesystem afterwards, to be able to use it.
Sincerely,
-Kenneth Straarup.
