(windows v1.03)
If you modify a sketch and save using "File->Save", it will save the file.
If you modify a sketch and then close Processing, a "semi-modal" dialog
will ask if you want to save, but it doesn't save your file.
If you modify a sketch and then create a new application, a fully modal
dialog will ask if you want to save, but it doesn't save your file.

steps:
-open processing, make a new sketch.
-type "ABC" and save it.
-close and reopen Processing.
-open the sketch --it was really saved. (says ABC)
-now, erase "ABC" and type "XYZ".
-now, click on the close button ("Save changes to xxxx? Y/N"), cilck yes.
-re-open Processing and the sketch (says "ABC" - it didn't save!)
-erase "ABC" and write "XYZ" again
-"File->New" ("Save changes to xxxx? Y/N/C"), click yes, a new sketch shows up
-re-open the original sketch (says "ABC" - it didn't save!)

(Sorry if this is a repeat of another bug. I personally have lost several
hours of work to this bug, and would like to spare others the same fate.)

*** This bug has been marked as a duplicate of 276 ***