I can confirm this behavior. (Using rectangular notes, 3/4 time sig, and grid = 1 or 2, REAPER v5.33)
One of the recent REAPER versions included an update in the snap-to-grid behavior when grid = 1 or longer, which is probably when this behavior sneaked in.
BTW, if I am not mistaken, grid=1 refers to one measure, not one whole note.
Perhaps try the latest v5.34 pre-release version:
v5.33: "+ MIDI: interpret grid lengths longer than the current measure length as a number of bars"
v5.34pre7: "+ MIDI editor: fix quantize when grid is a full measure or greater"
I quickly tested the new v5.34rc, and this has not been fixed.
Last edited by juliansader; 02-21-2017 at 03:31 PM.