If a table contains any column, which name is the same as reserved word (like "level", "index", "connect" etc.), then "Table->Data" tab fails to open with "ORA-00904: <column_name>:invalid identifier" error.
I know that having reserved words as column names is "wrong", but it's way too late to change our design, and it's still a rather serious bug that needs addressing.
I use SQLDev 4.0.0.13.80, Java 1.7.0_45 and our DB is Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 64bit.