I don't know, but my dd#2's second testing on the WISC-IV looked exactly like what you describe. She took the WISC at 7.5 and came out with a GAI in the upper 140s. B/c her CogAT was in the mid 1-teens and she was a very erratic achiever at school, we were told by her teacher at school that the IQ scores were wrong and due to good guessing. We were very unsure as to what was going on so we had her retested on the WISC and the RIAS a year later at 8.5. She also took the WIAT (achievement) at that time.
On the WISC at 8.5, she didn't reach discontinue guidelines for any subtest, but her GAI dropped 20 pts from a year earlier to the upper 120s. That was due primarily to the PRI dropping from the 99th percentile to the 75th percentile. Like your dd, she missed easy questions and got hard ones correct. The psych basically told us that she felt that the second set of IQ scores were correct and said that she had ruled out any LDs, ADHD, etc. She didn't have a good explanation for the drop in #s, though. Her RIAS was "uninterpretable" due to wide spread in scores and her WIAT scores were 2+ SDs higher than expected if the WISC score was correct.
I, obviously, don't have an answer for you as to whether this is a problematic scoring pattern or indicative of a misestimation of IQ, but I do have a similar situation here with dd.
My gut with dd is that she probably does have some mild degree of ADD as well as anxiety. I don't know if she is more gifted than MG, but we are currently proceeding as if she is MG until we see how she continues to progress emotionally, socially, and academically.
