A LastCellOfRowDummyRecord is returned after encountering a formula record that results in a string value. In particular I see this : if a formula(with string result) is encountered in the middle of a row and there is a missing cell immediately after - all cells upto the missing cells are reported as missing - probably because the LastCellOfRowDummyRecord resets the column number back to zero.
Are you able to produce a unit test that shows the problem? (Code with unit tests is much less likely to suffer accidental regressions!)
Created attachment 29099 [details] Excel File to reproduce 45672
Created attachment 29100 [details] Java class file to recreate the problem
Apologies, something went wrong and the attachments were submitted without my comments, so here goes : Attached a very simple excel file which has a formula at R1C3, this wrongly sets the missing columns.
This problem should be fixed in trunk. Please try with a nightly build - see download links on http://poi.apache.org/ or build yourself from SVN trunk, see http://poi.apache.org/subversion.html