wrong ordering of results with alpha-num strings

I had an issue when manually sorting a result set with alpha-numerical transaction ids.
Here is reduced sample:

``` SQL
SELECT x
FROM unnest(ARRAY[
'0AH700', '1CH859', '2LP231', '3NM022', '03P758', '3SF762',
'4FP507', '5VW585', '6M8723', '7VP948', '9AK289', '15U924',
'39M313', '61W694', '75E749', '141925', '300280'
]) AS x;
```


Start by reproducing the reduced SQL sample in Postico and inspect the result-set sorting entry point. Compare the displayed order with the expected ordering for the alphanumeric transaction IDs; done means manual sorting produces a confirmed, consistent order for this sample.

Written by the indexing model from the issue text.