I'm trying to insert a new row into an SDE/PostGIS database, using Python. The field is defined as numeric(38,8) in PostgreSQL, and as double in ArcCatalog. The decimal symbol in windows' language settings is set to '.'
I seem to remember we never found a fix, but decided to ignore it because the decimals weren't significant anyway (in our case). I would suggest you contact you local ESRI representative, it might be a bug. Who knows?
We made some tests and it seems that the problem is from ArcGIS Desktop side: if we change the Desktops Windows 7 Regional Settings from Portuguese (Portugal) format to English (United States), the decimal part of numbers is displayed,