It's consistent across most recordings, mainly when oboes double up the violin line on many larger scale pieces (eg. Messiah symphony/overture IIRC?) With period instruments it seems to change the character of the sound as if a new instrument has taken over, whereas with modern ones it just sounds like 2 different instruments paying the same notes.It's hard to tell what's causing your perception without measurements but you could be right. Was this with the period instruments vs modern ones playing the same score?
You can kind of feel it with Bach's concerto for oboe and violin but they don't play the same notes (ie counterpoint) so not as obvious.