The CRAN policy states
"Packages should not write in the users’ home filespace, nor anywhere else on the file system apart from the R session’s temporary directory (or during installation in the location pointed to by TMPDIR: and such usage should be cleaned up). Installing into the system’s R installation (e.g., scripts to its bin directory) is not allowed. "
"R CMD check" gave no indications of problems for my new package, but after submission to CRAN, the package was rejected for leaving files in /tmp.
Perhaps R CMD check could be improved by checking for these cases by either (1) monitoring file system access at a low level within R or (2) comparing the list of files in certain filespaces before and after.