SQLite Forum

null character sorts greater than 0x7f and less than 0x80
> In my case I discovered it was converting "mathematical fraktur capital a" into "ed a0 b5 ed b4 84" instead of "F0 9D 94 84" and PostgreSQL said "ERROR: invalid byte sequence for encoding "UTF8": 0xed 0xa0 0xb5". Passing through "Tcl_UtfToExternalDString(utf8encoding..." fixed it right up.

That looks like someone naively converted UTF-16 to UTF-8 and didn't handle the Surrogate pairs properly. The Unicode Standard requires that Surrogate pairs be processed by building the actual character and encoding that, not just the characters of the pairs individually. Many programs don't do the test right, and the need to test is somewhat what sort of security model you are trying to enforce, but PostgreSQL is right in rejecting it.