On the Schema Browser | Triggers Tab, comments are not visible if they are in the WHEN part of the trigger code, nonetheless Comments are still displayed by Toad Editor or SQL*Plus.
Schema Browser Script uses DBA_TRIGGERS to get the trigger code, if the comments are in the WHEN part of the trigger code, Oracle does not save the comments in DBA_TRIGGERS. The WHEN comments are stored in DBA_SOURCE, which is where the Editor and SQL*Plus get the script from. As long as the comments are not in the WHEN clause, they can be found on the DESCRIPTION column of DBA_TRIGGERS.
WORKAROUND: Move the comments down in the code so that they come after the BEGIN statement.
STATUS: Waiting for fix in a future release of Toad for Oracle.