The backslash substitution in PG is a non-standard postgres legacy and deprecated also in PG, but the extended syntax (with the preceding E) is supported.
There seem to be quite a few places, where the non-standard backslash substitution is used in OpenACS, see e.g. https://openacs.org/forums/message-view?message_id=544436
Sooner or later, we should address this.