I hit this issue recently, and it turns out to be in FAQ from procps:
Reference: http://procps.sourceforge.net/faq.html
The UNIX and POSIX standards require that user names and group names be printed as decimal integers when there is not enough room in the column. Truncating the names, besides being a violation of the standard, would lead to confusion between names like MichelleRichards and MichelleRichardson. The UNIX and POSIX way to change column width is to rename the column:
ps -o pid,user=CumbersomeUserNames -o comm
The easy way is to directly specify the desired width:
ps -o pid,user:19,comm
