Writing a string to to config can cause an old file to show up

This happened to me:

• BLE is activated.
• card10.cfg lists standard watch face as default app.
• Select Bluetooth as default app.
• Run the "Home" app.
• BLE app comes up and says that BLE is disabled.
• Exit BLE app and turn on USB storage.
• Text editor shows old version of card10.cfg with the BLE disabled and the default app still the standard watch face.
• Reboot card10.
• BLE app starts, says that BLE is enabled.
• Exit BLE app and turn on USB storage.
• Test exitor shows "new" version of card10.cfg with BLE enabled and BLE app as the default app.

Might be an artifact of my "modify a copy and then move file" implementation of writing an existing string to the config.

Maybe another option was a not correctly closed file? Or a not flushed buffer on LBA layer?