Ta, hadn't spotted that there was a new version out. I'll update to that.
Quick update I have just tried this same test [DB: 126.96.36.199.0 ] in version 19.1.0.094 / Build 094.2042 (fresh install no imported settings) and it still fails. I wonder why it worked for you? Could it be someting in the environment?
Either way, not a huge problem, it can be worked around easily enough.
I just revisited this on both 18.4 and 19.1, and I think I see what mislead me. When using Edit to add the virtual expression, we can explicitly select the column type or leave it with the default of <Derived>. Let's see what happens:
produces DDL which includes the MODIFY statement:
Now explicitly select the column type to be NUMBER:
which excludes the MODIFY in the DDL:
So in my other reply, I must have just set the column type to NUMBER without there being any particular fix that went into the editor for 18.4.
Sorry for the confusion!