Comment 2 for bug 108571

Here is some PM_DEBUG message (linux-source-2.6.20.3/Documentation/power/s2ram.txt)

...
[ 16.314911] ACPI: (supports S0 S1 S3 S4 S5)
[ 16.315204] Magic number: 0:150:167
[ 16.315247] hash matches drivers/base/power/resume.c:28
[ 16.315340] hash matches device ttyq7
[ 16.315549] drivers/rtc/hctosys.c: unable to open rtc device (rtc0)
...

It is alway connected with some "tty??" device...