After further play, I see my issue is the same as : Unmatched trio highlighted as if they will match
I was wrong, the spell doesn’t give any wrong gems. The actual issue is affected by scorpions giving me yellow gems from the defense Hiding in Sand.
The actual issue is that when using Split Skulls, the gems fall from above and sometimes make a match. The match then “freezes” with the said matched gems getting a pulsing background showing which gems will not move in the future. Then the skulls are created and can be created in the matched sets. When this happens the set is no longer matched, but remains “frozen” with the new skulls having a background denoting that they cannot be moved either.
Is this a bug or a very annoying mechanic that can make matches extremely difficult? You cannot move the unmatched gem out of the matched position in order to make a correct match, and are forced to make matches of the gems in their frozen state in order to clear them from the board.