This is an issue I haven't met with, but with what you say I think it could be studied further.
Would you tell us what preferences are selected in Menu > Edition > Preferences > Volume Management, and then close PCManFM, start it from a console (just invoke "pcmanfm" as is) and repeat the steps that make you meet with left icon disapearance while file icons are still there ?
If the same bug happens, what is in the console as messages and do a screeshot too ?
When you are going to unmount, click the back button until you are in the folder you opened the device in. Unmount and you will see "emptiness."
Howard, is it that the directory which is displayed is changed to elsewhere, (your home ?) or is it the files that are in the usb stick or mp3 stick that are displayed ?
// I noticed a tendency of PCManFM 2 that does not refresh the directory which is displayed, sometimes.
// PCManFM 2 is a 0.9.7 version, much better than the former 0.5.2 that has been recoded from scratch, but it's not a 1.0 yet, so each bug reported will help the developer to improve it.