It may seem like a simple question, but we believe that there is some sort of bug/error in Maple that is interfering with Maple's capability to save as Classic.
I apologize that I have not been able to devise a method to exactly reproduce this result. It's hit-or-miss. It seems to be the case that this error crops up in Classic worksheets (and, in theory, would happen on a Windows machine if one were to open and edit a Classic worksheet in Standard Maple).
On Linux and Mac (OS X 10.04) machines, when we open a Classic worksheet, edit it, and try to save (just Save, not Save As. Just ctrl+s or apple+s), the warning dialogue box will come up telling us that there may be elements in the worksheet not compatible with the Classic worksheet format. We select Ok and the worksheet is supposed to save at this point; however, there are many times that it will not save. If we immediately try to save again, it will usually save that time.
Out of 20 worksheets that I just edited, 15 required me to save twice, and 2 required me to save three times before it actually saved.
Any ideas on why this is happening?