Random motion and lost steps after upgrade

Also little update from my side.
I did some tests the past days but with no results so far. Have done some fake millings for ~90 minutes with no problems and also some real millings for ~60 minutes with no problems. No changes in hardware/software or configuration. It is just strange..

However, as soon as I have something really reproduceable I keep you posted.

BTW: In case the cutter crashes again I usually press the emergency stop at the machine which also stops the program.
Are there any special logs I should then make a copy ?

Cheers

Now it happend again but this time I saw the problem.

Did some millings with two cutters whereby in the middle I did a tool change and some tool length compensations.
For this I wrote a little sub. So during tool length measuring LinuxCNC got it's new values, ---tried to bring the cutter to a save layer--- but here only thing that happend is that the cutter went a little bit into that direction and a "tweeting" (not sure how to translate; Opossite of "bass") sound came from the z achsis. Rest is then clear; LinuxCNC thought that the cutter is at a complete different Z position and tried to move the cutter deeper and crushed into the workpiece. So far so bad.

What did I check now:
- No warnings so far about real-time problems (the little window in the down right corner at achsis...)
- Kernel is still "3.4-9-rtai-686-pae #1 SMP PREEMPT Debian 3.4.55-4linuxcnc i686 GNU/Linux"
- Paramters for Z-Achsis:
MAX_VELOCITY = 129.0
MAX_ACCELERATION = 1000.0
STEPGEN_MAXACCEL = 1250.0
Engines are on X/Y/Z the same. I had adjusted the velocity to 50% some time ago because I do not need that much speed here at all. Paramters should be according to machine specs.

Any ideas ?

NOTE: For the moment I adjusted the values to be at 50%. Maybe it helps... However, strange is that the problem is only with the Z-Achsis and only very seldom.