Powerpoint writes corrupt PPT files

[legsak1mbo]

We've found this only affects PPT files (not PPTX) when writing to the Dot net Mirror. And even then it's only certain PPT files - it seems to be PPT files created with older versions of Powerpoint. The file that we've been testing with is at http://manoa.hawaii.edu/ctahr/aheed/Carl/13-Using_Powerpoint.ppt

When compared with the C mirror the PPT file is 512 bytes too short when written and once the file is closed Powerpoint then refuses to re-open it. Powerpoint does not report any errors during the save.

We've debugged the writes and everything appears normal until about half way through when small 2 byte differences begin to appear.

Adding a stream.Flush after the stream.Write in the WriteFile method seems to resolve this but this seems like more of a hack than a fix.

Keen to get your thoughts and can provide more information as needed.