The problem appeared again, so here are the (hopefully helpful) backtrace (attached) and the output of strace:

~$ strace -p 7238
attach: ptrace(PTRACE_ATTACH, ...): Operation not permitted
ivailo@darkstar:~$ sudo strace -p 7238
Process 7238 attached - interrupt to quit
gettimeofday({1172324704, 520340}, NULL) = 0
gettimeofday({1172324704, 520494}, NULL) = 0
poll([{fd=7, events=POLLIN}, {fd=9, events=POLLIN|POLLPRI}, {fd=11, events=POLLIN|POLLPRI}, {fd=14, events=POLLIN|POLLPRI}, {fd=16, events=POLLIN|POLLPRI}, {fd=17, events=POLLIN|POLLPRI}], 6, 4917) = 0
gettimeofday({1172324709, 443822}, NULL) = 0
time(NULL)                              = 1172324709
time(NULL)                              = 1172324709
gettimeofday({1172324709, 444222}, NULL) = 0
poll([{fd=7, events=POLLIN}, {fd=9, events=POLLIN|POLLPRI}, {fd=11, events=POLLIN|POLLPRI}, {fd=14, events=POLLIN|POLLPRI}, {fd=16, events=POLLIN|POLLPRI}, {fd=17, events=POLLIN|POLLPRI}], 6, 30000) = 0
gettimeofday({1172324739, 449479}, NULL) = 0
time(NULL)                              = 1172324739
time(NULL)                              = 1172324739
gettimeofday({1172324739, 449884}, NULL) = 0
poll([{fd=7, events=POLLIN}, {fd=9, events=POLLIN|POLLPRI}, {fd=11, events=POLLIN|POLLPRI}, {fd=14, events=POLLIN|POLLPRI}, {fd=16, events=POLLIN|POLLPRI}, {fd=17, events=POLLIN|POLLPRI}], 6, 30000) = 0
gettimeofday({1172324769, 455873}, NULL) = 0
time(NULL)                              = 1172324769
time(NULL)                              = 1172324769
gettimeofday({1172324769, 456281}, NULL) = 0
poll([{fd=7, events=POLLIN}, {fd=9, events=POLLIN|POLLPRI}, {fd=11, events=POLLIN|POLLPRI}, {fd=14, events=POLLIN|POLLPRI}, {fd=16, events=POLLIN|POLLPRI}, {fd=17, events=POLLIN|POLLPRI}], 6, 30000) = 0
gettimeofday({1172324799, 462835}, NULL) = 0
time(NULL)                              = 1172324799
time(NULL)                              = 1172324799
gettimeofday({1172324799, 463245}, NULL) = 0
poll([{fd=7, events=POLLIN}, {fd=9, events=POLLIN|POLLPRI}, {fd=11, events=POLLIN|POLLPRI}, {fd=14, events=POLLIN|POLLPRI}, {fd=16, events=POLLIN|POLLPRI}, {fd=17, events=POLLIN|POLLPRI}], 6, 28260) = 0
gettimeofday({1172324827, 730052}, NULL) = 0
gettimeofday({1172324827, 730189}, NULL) = 0
poll([{fd=7, events=POLLIN}, {fd=9, events=POLLIN|POLLPRI}, {fd=11, events=POLLIN|POLLPRI}, {fd=14, events=POLLIN|POLLPRI}, {fd=16, events=POLLIN|POLLPRI}, {fd=17, events=POLLIN|POLLPRI}], 6, 1) = 0
gettimeofday({1172324827, 738199}, NULL) = 0
gettimeofday({1172324827, 738329}, NULL) = 0
poll([{fd=7, events=POLLIN}, {fd=9, events=POLLIN|POLLPRI}, {fd=11, events=POLLIN|POLLPRI}, {fd=14, events=POLLIN|POLLPRI}, {fd=16, events=POLLIN|POLLPRI}, {fd=17, events=POLLIN|POLLPRI}], 6, 1725) = 0
gettimeofday({1172324829, 470283}, NULL) = 0
time(NULL)                              = 1172324829
time(NULL)                              = 1172324829
gettimeofday({1172324829, 470689}, NULL) = 0
poll([{fd=7, events=POLLIN}, {fd=9, events=POLLIN|POLLPRI}, {fd=11, events=POLLIN|POLLPRI}, {fd=14, events=POLLIN|POLLPRI}, {fd=16, events=POLLIN|POLLPRI}, {fd=17, events=POLLIN|POLLPRI}], 6, 30000) = 0
gettimeofday({1172324859, 478181}, NULL) = 0
time(NULL)                              = 1172324859
time(NULL)                              = 1172324859
gettimeofday({1172324859, 478598}, NULL) = 0
poll([{fd=7, events=POLLIN}, {fd=9, events=POLLIN|POLLPRI}, {fd=11, events=POLLIN|POLLPRI}, {fd=14, events=POLLIN|POLLPRI}, {fd=16, events=POLLIN|POLLPRI}, {fd=17, events=POLLIN|POLLPRI}], 6, 30000) = 0
gettimeofday({1172324889, 486493}, NULL) = 0
time(NULL)                              = 1172324889
time(NULL)                              = 1172324889
gettimeofday({1172324889, 486911}, NULL) = 0
poll( <unfinished ...>
Process 7238 detached
======================================
NOTE: the strace was interrupted via CTRL+C