I try input weight manualy as usually and now Garmin Connect says: BAD REQUEST.
Win7 64bit, Chrome Version 35.0.1916.114 m
I have an other workaround when you change the decimal representation in your settings to "1,234.56" it works in the health tab when using something with "." as decimal separator. So it seems the website is locally rendered with german locale things and the "1.234,56" number format but the server did not accept the "," and rejects this. When changed in the preferences to use a "." in the representation it works.