Thank you Victor. Perhaps I'll build a 3.10-rt for Ubuntu Studio later,
using my own config, to see if it does behave different, than it does for
Arch Linux. I guess the default config by the AUR package is like my own
configs usually are. I planned to use different configs with Arch, one
e.g. without HR timer enabled, but since I experience those other issues,
I won't do it for Arch and the 3.10-rt patches that are released until
now. Regards, Ralf