Not a kernel issue. Your ttyC10 - ttyC15 are not "legal" tty names in
Linux.
Actually, it's an application issue. Modern /usr/include/utmp.h files
already leave enough space for four character ut_id fields, and "ttyC10"
only requires a three character ut_id field (i.e., "C10")
The problem is that there are some old programs which still assume that
a two character ut_id field. Fortunately, this is fixable with source
code, quick edit, and a fast recompile.... In the future, hopefully new
distributions will be lift this restriction soon.
- Ted