There's a Dark Pharaoh (of course) Science Building encounter where a Mi-go attacks you and if you fail a Speed (-2) check "[...] it seems to move with preternatural speed, and you may not use any investigator cards in this encounter."
Zoey Samaras wandered into this encounter last night ... while Cursed. Obviously the knife, and the cross, and the Bravery skill, etc. were all unusable, but the Curse itself is an investigator card. 2 dice Horror check, followed by a 2 dice Combat check, both needing to pass first time to avoid losing, and no clues.
Fortunately they got a 6 on both rolls, so it didn't come up, but ... by the strict wording, Curses shouldn't count in the fight (and neither should blessings, which are perhaps more common, so it's not as if you gain an overall advantage playing this way) ... on the other hand "it moves so fast your bad luck doesn't have time to affect the outcome" makes no sense!
(Similarly, what about personal story pass/fail cards - or what about the conditions? If Patrice fails the Speed check, is she prevented from putting a token on her PS because it's an Investigator card and the Unique Item was gained while it was unusable?)