Spreadsheet::Read just uses what is available to parse the source given, and prefers Spreadsheet::ParseXLSX over Spreadsheet::XLSX unless specifically told to use the buggy module, which is supported because it can be supported (and because the better module did not yet exist when the buggy module was readily available when I started Spreadsheet::Read. It so only relies on (bad) modules if there are no better alternatives available.

If you find bugs, real bugs, in the parser, make a ticket. If you find bugs in the wrapper as it does not deal with the parser correctly, let me know.

I am working with Corion to get his new parsers for ODS supported too, but that is currently too unstable.

As I use XLSX for quite a number of (big) jobs, I am fairly certain it behaves well. I must admit that I never had to deal with buggy custom formats, so I never hit any trouble.