Why ra-VU in Numbers 20:13?
Numbers 20:13 (with my own, loose translation):
הֵמָּה מֵי מְרִיבָה אֲשֶׁר רָבוּ בְנֵי יִשְׂרָאֵל אֶת ה׳
This was the Fight Water: the Jews fought God
The word "רָבוּ" ("fought") has its stress on the last syllable, ra-VU, rather than the first, RA-vu.
This would seem to imply that its root is רבה. The verb with root ריב would have past tense RA-vu. (I can't find a good Jewish source for this fact, but Gesenius implies as much in §§72b, 73a, 75h. The context surrounding those will prove helpful to understanding them.)
Yet all the commentaries seem to read the word as from the root ריב, "fight" (as indeed seems obvious from the context).
(I've checked various commentaries, including מנחת שי, הכתב והקבלה, and העמק דבר, but have found no explanation.)