I've had this problem with several different anise spirits and once with St. Antoine, but never heard about it anywhere. Some time (and usually several glasses) after opening the bottle, they didn't louche (other than the very slightest haze) when ice water was added, unless the bottle was shaken beforehand. It seems like the anethole content tends to dehomogenize under certain conditions, or something like that. It's even more likely to happen with home filled 1.5 oz. sample bottles.
In the case of St. Antoine, it was even before half of the bottle was gone. The bottles arrived lukewarm, if that counts, but only the Antoine had this issue. Curiously the non-louching glass came just some twenty minutes after a perfectly louched one. (I never dared to pour another Antoine without shaking the bottle.)
Any experiences or ideas on why it happens? I rather wouldn't shake my bottles...