When the check for word repetitions is enabled, texstudio also complains about repeated variables in math mode, e.g.
$\sum_{v \in V} \lambda_v v$. Probably it would be best to completely disable the check in math mode, since it does not really make sense there.
We were kind of waiting for qcodeedit 3 for that, since with qce3 it would be much easier to detect which words are math words and which not.
Ok, then I'll wait until that version is released! :)
Actually there is an easy hack to hide the errors.
(although it will still do the grammar checking, just not showing the errors)