Does this make sense?

Yes, that is quite possible

I was taking the GMATPrep yesterday and got 5 SC wrong out of 8 while may usual ratio is 1 out of 5. However, I've made almost no mistakes in RC and CRs that's way I have to agree with the previous comment. The better you do these sections, the more idioms and other pretty things you will get!

Look at the difficulty level of the questions you got wrong. I think Manhattan cat provides that information. Score is a factor of number of correct answers and difficulty level.

I am almost 100% sure that the CAT you are talking about is GMATprep2. If that's the case we are experiencing similar trouble. I have taken GMATprep many times and I found that GMATprep2 contains some really tedious SC's making its verbal part significantly harder than that of GMATprep1. I dont now neither why that is happening nor the correlation among GMATprep1, GMATprep2 and actual test, this is rather my observation as an experienced GMATprep user.
Also, I found that GMATprep2 has math section that is slightly (but very, very slightly) easier than that of GMATprep1. Maybe it is not easier at all but contains some questions that I'm comfortable with. Again, without any deep analysis of the cause, I observed that it is slightly easier for me to obtain Q51 on GMATprep2 than Q50 on GMATprep1. Of course, this difference is not so obvious and so severe as for verbal parts of 1 and 2. Verbal is, IMO, much harder on GP2.
Should this worry us? I don't know. I have no clue what is more representative of the real deal. Has anyone experienced something similar?

interesting observations...thanks!

Yes, that was GMATPrep2

Yes I was speaking about GMATPrep2 also! It was weird b/c I did so well on both CR and RC this time and I suck at those usually...I guess I can attribute that to the extra studying I've been doing on Verbal, but I was really concerned about the SC. Thanks for your input!