So it appears that something is misbehaving in a manner specific to OS X. Someone should enter this in bugzilla.
Done, see http://bugzilla.lyx.org/show_bug.cgi?id=4197
A wild guess is that the 9 relates to the cell divisor being interpreted wrongly on the Mac platform. This is further indicated by selecting two cells in a column (i.e. above each other) copying and pasting. This results in apaapa, i.e. without the 9.
/Anders
