Please review the article RPM file naming as background to this article.
Sometime on or around version 126.96.36.1991, a bug was unintentionally introduced which converted the ASCII space character to an underscore during output.
A customer found their jobs which previously had been named correctly from the information found in the LPR control file were now being named with the spaces changed to underscores and brought it to our attention. Because the ASCII space character is a valid filename character in Windows file systems, our development team agreed it was not working as intended and it was quickly resolved. As a result, the space character is once again allowed in filenames RPM generates.
This bug was not documented on our development roadmap. In fact, not all bugs end up there for a variety of reasons including simple oversight, whether the bug is determined significant or not, or if the bug is both introduced and resolved between official releases.