What it means is that for the first part you'll be "phased" and obviously untouchable.
After the phased part of the power is gone you *the caster* becomes unphased back into reality and can be attacked. However you'll still have the +jump component that you get from the power (only reason to keep it active 2bh), then you become re-phased after 90 seconds like you said.
So not a bug really 
Perhaps need better wording though.
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The wording in the description says that i should be phased for 30 seconds, un-phased for 30 seconds, then phased for 30 seconds (repeat, rinse) till i toggle the power off. If it is indeed supposed to be un-phased for 90 seconds (which is how how long i'm being un-phased for at the moment as oppose to the 30 seconds stated) it definately needs re-wording.
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Nebulous Form states that "After 30 seconds the phase out effect will wear off. 30 seconds later, if this power is still active the user will become phased out once again". I've just timed it, and i phase for 30 seconds, then i'm not phased for 1 and a half minutes before phasing again.
Is the description wrong? Should it read phase for 30 seconds then wait 90 seconds before phasing again? Or is the timing out?
Help Dirk Knightly the freelance detective solve a case in Arc ID:368097