The SGF specification, states ( http://www.red-bean.com/sgf/sgf4.html ) that
Only one of each property is allowed per node, e.g. one cannot have two comments in one node: ... ; C[comment1] B [dg] C[comment2] ; ... This is an error.
This is unfortunately precisely what OGS does. When players post multiple comments within one move, these are added in separate C[comment] properties, while they should be merged.
Example can be seen e.g. in (3 comments at the end):
Anyways, thanks for an awesome Go site.