Looks funny Never seen them do that for the reason mentioned. Mine never done it - none of my great many synos ever done this. Swimming upside down they did plenty of... but laying like this... Peculiar! Interesting to know.
Looks like the true decora - maxillary barbels are clearly branched.
Hes the only one who does it, neither of the standard synos or the two pleurops synos do it.. and normally he disapears as soon as a get the camera out but got away with it this time!