Oh my god ....
I started with 63 and Mana Tombs tonight and finally swapped my second mage with my shadow priest and had to set up a macro for him since my elemental shaman and ice mage were played completely different without macros.

Code:
/castsequence [nochanneling:Mind Flay] reset=34 Vampiric Embrace, Shadow Word: Pain, Vampiric Touch, Mind Blast,  Mind Flay, Mind Flay, Mind Blast, Mind Flay, Mind Flay, Mind Blast, Vampiric Touch, Mind Flay, Mind Blast
Despite the fact that the sequence itself may be crap .... this doesn't matter. What matter is that adding target or combat or both totally screw up the complete macro ->
Code:
... reset=target/34 ...
or
Code:
... reset=34/target ...
or
Code:
... reset=combat/target/34 ...
or
Code:
... reset=target/34/combat ...
From a perfectly working sequence with reset=34 I come to a mentally challenged macro which "spams" Vampiric Embrace with adding target or combat.
-> Vampiric Embrace, *spamming the button*, I see the cooldown run down and the message like "can't cast that spell now", *spamming the button*, the cooldown runs out, Vampiric Embrace, *spamming the button*, I see the cooldown .....

Removing the reset-condition and just leaving the time of 34 seconds in my case helps.

So did anybody figure out why this is like it is?

Xorn