instead of wasting calories having you dig through things or doing a re-install, I would advise you to go get version 4.1.3. It's newer and stabler than 4.0.2.
I'm afraid installing 4.1.3 is as also expensive in calories as it requires installing Java 8 and I have security restrictions on my system - I try anyway, but in the meanwhile I'm wondering which parameters or data Sqldev is using to do this conversion...
I managed to install 4.1.3 : the issue is the same.
Problem solved with 4.1.3 : we had a change in our nls_session parameters that passed the NLS_NUMERIC_CHARACTERS to comma instead of dot.
To avoid the syntax error of mixing decimal commas with separation commas, SqlDevelopper framed them into quotes, and in the moment of executing the insert query, the decimal values were refused by a differently parametered session...
alter session set NLS_NUMERIC_CHARACTERS = '. ';