Spell-Checker craziness

In a post on a message board, when I used the word when I typed de-incentivised it was underlined by the spell-checker in spite of being a perfectly good word and the suggested alternatives were

DE-incentivised
De-incentivised
d-incentivised
ed-incentivised

and

e-incentivised, none of which look like real words.

But it got stranger. When I posted a humourous aside mentioning this fact, all of these suggested alternatives were also marked as wrong, in spite of being the very things the spell-checker told me to use. Intrigued I probed further and the suggested list of alternatives for these words included

DE-incentive's
DE-incentive
DE-insentience
Incentive's
incentive's
De-incentive's
De-incentive
De-insentience
d-incentive's
d-incentive
d-insentience
distinctiveness
ed-incentive's
ed-incentive
ed-insentience
e-incentive's
e-incentive
and
e-insentience

none of which got underlined but most of which don't look like real words to me either.

I love spell-checker!