This may be normal behaviour, but worth noting in case not.
Importing a saved bank overwrites the original bank - and does not write over the currently selected bank.
For example: I exported and saved Bank 3. loaded a patch in an empty Bank 12 then loaded the saved bank. I assumed it would load the saved bank into the current bank 12, but it replaces the original Bank 3.
Also, the synth loads a random patch when importing the saved file.
How are you getting it to import/export only Banks? That would be really sweet! 
(We’re talking about the Librarian page, with the buttons on the left side?)
I know the buttons have “bank” in their names, but I believe they’re really doing Bulk Dumps – dumping everything!
Also, it’s a direct connection between the Sub37 and a file on the disk – the editor doesn’t do anything with the data other than pass it through.
Also, the import/export notation confuses me a little, since I expect the terms to refer to what the editor does. But “Export” means bulk dump from S37 to disk, and “Import” is disk to Sub37. It requires a shift in point-of-view from the editor to the hardware. I’m in the editor clicking buttons; “Export” from here would imply the editor sending something to the Sub 37. No, we first pretend we’re on the hardware, so an “export” means a bulk-dump to the file-system on the computer.
Sorry for being chatty.
I hope Gil will come along and correct me.
EDIT - Jan 8
I’m wrong above when I called them Bulk Dumps. It’s not, it’s an “All Presets Dump”. Which is kind of strange…
It may well be doing dumps of all the preset data - I presumed it was banks only, as that is how it’s labelled.
This would explain why Bank 12 remained unchanged!