I mount n-in-one card readers as a volume under a drive letter such as V:\Siig_CardReader. When I pull the SD card from the card reader the drive letter disappears from the Tree View and the top toolbar drive list. I need to exit MC and restart it to get drive back. Of course Windows Explorer acts correctly in this case, nothing disappears, just the "Siig_CardReader" can't be read or entered.
The behavior is similar to when I eject a DVD from a drive - the DVD drive letter goes away until I put in a new DVD. Unfortunately the alg needs to be smarter for mounted volumes under a drive letter.