Read-only properties.

I'm using WinXP Home SP2.

I ran across this problem while using an external hard drive. Windows
Explorer has no problem moving data to the drive, but *some* programs refuse
to write to it, suggesting that I check read-write status, authority, etc. I
ASSUME that it's because the properties of the destination show a check in
the Read-only box, albeit the check mark appears to be dimmed, and not solid
black. It doesn't help if I remove the mark and apply the options in the
following screen. Not only that, but the next time around the dim
check-mark is back. Other programs don't object, and write to the drive as
usual. (I did not experiment the same way with the internal hard drive, but
I can't recall ever getting the same rejection except when it was clearly
legitimate.)

The Help system didn't have anything to say about Read-only. Can somebody
expound on this for me?