Hi aom12,
The Quant and Verbal Scaled Scores that each GMATer receives in the Official Score Report are 'rounded' numbers (for convenience); the ACTUAL Scaled Scores are almost never integers though - and it's those actual results that are used to calculate the Overall GMAT Score (out of 800). Since you scored a Q49, I assume that you know the 'rules of rounding'; in the context of the numbers you've listed though, here's how we can account for those results:
A Q49 could actually be any result from a Q48.5 - Q49.4, whereas....
the difference between a V38 and a V39 might be relatively minuscule by comparison (re: a V38.4 and a V38.5).
Thus, in your example, the 10-point difference in the Overall Scores is almost certainly due to really close Verbal results but a significant-enough difference in the Quant results.
GMAT assassins aren't born, they're made,
Rich