In SFmpqapi there was a bug in the code that looks for free hash table entries when you add or rename files in an MPQ that could prevent adding or renaming files if every hash table entry had previously been used, even if files are deleted. A fix for this has been uploaded and a new build packaged with WinMPQ. Though maybe not useful for many, the build packaged with WinMPQ is now compatible with Windows 9x again (until recently, I was not aware that I had broken compatibility).
There was also a bug that did not affect WinMPQ but would affect programs that attempt to use file seek operations that do not use the beginning of the file as the reference point.
For developers using SFmpqapi and wanting to use a more current version, for a long time it has been necessary to either use the DLL bundled with WinMPQ or compile your own from source. Today I have uploaded a set of new binaries and the latest header files for those who prefer using the binary package rather than compiling their own.
I have also added a link in the downloads page to the cwad library that WinMPQ uses. It has existed in the download folder on this site and the link had been given out on some forums, but until now I had not added a link on the downloads page. A new version has been uploaded that fixes the same seek bug SFmpqapi had and prevents a lockup that can happen when listing files from an empty cwad archive. The new version has been added to the WinMPQ package.