DISK_ERR persists following re-insertion of microSD card

This is a follow on from my previous discussion concerning the microSD card.

With all my bits and pieces connected up and working, when I run the following command, assuming a text file called test.txt is already on the microSD card which contains the word hello followed by an empty line:

>var f = require("fs").readFile("test.txt");
="hello\n\n"

If, while my system is running, I remove the microSD card and re-run the above I get the following response:

>var f = require("fs").readFile("test.txt");
ERROR: Unable to read file : DISK_ERR
=undefined

replacing the card and re-running the same command still produces the DISK_ERR.

My questions:

• Is this expected behaviour?
  
• Should I implement error checking to prevent getting this error upon re-inserting the microSD card while the system is live?
  
• If so, any suggestions how?
  
  

Temporary solution
The only way I can get the read to work again is to reset everything.