Core dumps after dismount of time machine volume

My /cores folder is regularly filled with core dumps of about 200 MB size. This happens apparently every time when time machine tries to backup but the TM volume has been dismounted.
The parallels.log then has an entry like the one copied below.
If I disable TM nothing happens.
This problem is particularly annoying since there might by about 100 core dumps a day, which eats up the free disk space rather quickly, but the /cores folder is usually invisible!
Any help is welcome.
-Reiner

01-14 09:04:28.877 F /disp:175:6a0f/ On enter : dev_type = 6 dev_name = IOMedia event_code = 0
01-14 09:04:28.933 F /disp:175:6a0f/ On exit : dev_type = 6 dev_name = IOMedia event_code = 0
01-14 09:04:29.344 F /disp:175:6a0f/ On enter : dev_type = 15 dev_name = event_code = 0
01-14 09:04:29.419 F /disp:175:6a0f/ Usb device disconnected 24160000|1058|0704|high|--|575845393038554137323231
01-14 09:04:29.419 F /disp:175:6a0f/ make post to autoconnect event from thread notifier! strDevImage == 24160000|1058|0704|high|--|575845393038554137323231 uiDevState==0
01-14 09:04:30.151 F /disp:175:6a0f/ On exit : dev_type = 15 dev_name = event_code = 0
01-14 09:04:30.151 W /disp:175:6a0f/ Network setting was changed for 6 network subclass, event 4, if_name en10
01-14 09:04:30.151 F /disp:175:6a0f/ On enter : dev_type = 8 dev_name = en10 event_code = 1
01-14 09:04:30.205 F /disp:175:6a0f/ On exit : dev_type = 8 dev_name = en10 event_code = 1
01-14 09:04:31.471 W /disp:175:6a0f/ Network setting was changed for 6 network subclass, event 1, if_name en10
01-14 09:04:31.471 F /disp:175:6a0f/ On enter : dev_type = 8 dev_name = en10 event_code = 1
01-14 09:04:31.565 F /disp:175:6a0f/ On exit : dev_type = 8 dev_name = en10 event_code = 1
01-14 09:04:32.703 W /disp:175:6a0f/ Network setting was changed for 1 network subclass, event 1, if_name en10
01-14 09:04:32.703 F /disp:175:6a0f/ On enter : dev_type = 8 dev_name = en10 event_code = 1
01-14 09:04:32.780 F /disp:175:6a0f/ On exit : dev_type = 8 dev_name = en10 event_code = 1
01-14 09:04:36.140 F /disp:175:6a0f/ On enter : dev_type = 15 dev_name = 24160000 event_code = 1
01-14 09:04:36.210 F /disp:175:6a0f/ Usb device connected 24160000|1058|0704|high|--|575845393038554137323231
01-14 09:04:36.210 F /disp:175:6a0f/ make post to autoconnect event from thread notifier! strDevImage == 24160000|1058|0704|high|--|575845393038554137323231 uiDevState==1
01-14 09:04:36.211 F /disp:175:6a0f/ make post to autoconnect event from thread notifier! strDevImage == 24160000|1058|0704|high|--|575845393038554137323231 uiDevState==1
01-14 09:04:36.211 F /disp:175:6a0f/ usb device with id == 24160000|1058|0704|high|--|575845393038554137323231 removed from list excluded of autoconnect
01-14 09:04:36.236 F /disp:175:6a0f/ On exit : dev_type = 15 dev_name = 24160000 event_code = 1
01-14 09:04:37.207 F /disp:175:6a0f/ On enter : dev_type = 6 dev_name = IOMedia event_code = 1
01-14 09:04:37.275 F /disp:175:6a0f/ On exit : dev_type = 6 dev_name = IOMedia event_code = 1
01-14 09:04:38.934 F /disp:175:6a0f/ On enter : dev_type = 6 dev_name = IOMedia event_code = 1
01-14 09:04:39.160 F /disp:175:6a0f/ On exit : dev_type = 6 dev_name = IOMedia event_code = 1
01-14 09:04:39.161 F /disp:175:6a0f/ On enter : dev_type = 6 dev_name = IOMedia event_code = 1
01-14 09:04:39.373 F /disp:175:6a0f/ On exit : dev_type = 6 dev_name = IOMedia event_code = 1
01-14 09:04:39.373 F /disp:175:6a0f/ On enter : dev_type = 6 dev_name = IOMedia event_code = 1
01-14 09:04:39.520 F /disp:175:6a0f/ On exit : dev_type = 6 dev_name = IOMedia event_code = 1
01-14 09:04:48.929 F /cmn_utils:11478:20b/ ParallelsDirs::Init( ) was called. Current app mode = 1 ( DESKTOP_MAC ) build version: 6.0.11992.625546 Mon, 20 Dec 2010 22:24:04
01-14 09:04:48.930 F /prl_naptd:11478:20b/ Current maxfiles_limit is 1024 (sys_val=1024)