ignore ownership on this volume not persistent

SoftRAID does not impact what is inside the volume. Yes this would be supported in a SoftRAID volume.

Maybe your info database is damaged.
Try this:
Use "Go to Folder" and paste this in:
/private/var/db/volinfo.database

Open the volinfo database with a text editor like BBEdit, text Wrangler etc.
It should be a list of numbers and settings like this:

37A311270B033E90: 00000001
EAE5AC229A3175C6: 00000001
D95C49B4C980F617: 00000001
16A6711A3F0B136A: 00000001
C16E811E38C5FB8A: 00000001
8BCC14B85F9BE098: 00000001
E04E069E4DA0AA84: 00000001
BB4CC66EACC96B1C: 00000001
E6AA79982F83B305: 00000001

If it is damaged, then it may look like this:

37A311270B033E90: 00000001
EAE5AC229A3175C6: 00000001D95C49B4C980F617: 00000001
16A6711A3F0B136A: 00000001
C16E811E38C5FB8A: 00000001
8BCC14B85F9BE098: 00000001
E04E069E4DA0AA84: 00000001
BB4CC66EACC96B1C: 00000001
E6AA79982F83B305: 00000001

See if any of the entries are missing a
If so, add the return and save the file.
See if this fixes your problem.

Sorry for the late reply to your answer. I could not follow-up this matter earlier due to new family member...

I examined the file in "/private/var/db/volinfo.database" as suggested and I cannot recognize the described error.

Here is the file content:

704A68F7F16DD625: 00000001
2A32D1D4EBF620B7: 00000001
91B6008B56F22261: 00000001
F1D00727395B4543: 00000001
CDFB1604CECD2839: 00000001
BFA4B641FBD1A653: 00000001
36603CF7737080A5: 00000001
B60E4832F011CE29: 00000001
9C158B642517D651: 00000001
4F00A4E56B4F2309: 00000001
7B142F2A169B9CCC: 00000001
B60E4832F011CE29: 00000000
B60E4832F011CE29: 00000001
B60E4832F011CE29: 00000000
19C036F2BBFAD618: 00000001
CCD05313F57D6935: 00000001
19C036F2BBFAD618: 00000000
19C036F2BBFAD618: 00000001
0370988A7D5D94EF: 00000001
201DD87BA5E269D4: 00000001
0370988A7D5D94EF: 00000000
0370988A7D5D94EF: 00000001
C5E2735E5EA04E05: 00000001
65033E1D73AAFD7C: 00000001
E5401CCB33E622E6: 00000001
E1D5035AD575E2B5: 00000001
E5401CCB33E622E6: 00000000
E5401CCB33E622E6: 00000001
70CD6CD4C9925F68: 00000001
478BA05ABEEDFE7F: 00000001
7A0B44E3E281CB21: 00000001
70CD6CD4C9925F68: 00000000
70CD6CD4C9925F68: 00000001
4EC5D85460C4C7D9: 00000001
4E67870DFF9BC2D4: 00000001
29C15C839EE1D20C: 00000001
4EC5D85460C4C7D9: 00000000
4EC5D85460C4C7D9: 00000001
70CD6CD4C9925F68: 00000000
70CD6CD4C9925F68: 00000000
70CD6CD4C9925F68: 00000000
70CD6CD4C9925F68: 00000000
24CFC0DA-FA76-34DD-ABE3-6141CCF8E269: 00000000
24CFC0DA-FA76-34DD-ABE3-6141CCF8E269: 00000000

The problem is not solved.
After each restart the "ignore ownership" option on my stripped volume is switched-off again.
I use the current SoftRaid version5.5.5 and latest Mac OS 10.12.2 (16C67)

I don't think these lines should be in this file:
24CFC0DA-FA76-34DD-ABE3-6141CCF8E269: 00000000
24CFC0DA-FA76-34DD-ABE3-6141CCF8E269: 00000000

It is safe to delete this file completely. Then restart and Set the permissions on the volume correctly. See if that fixes this problem.

Thank you very much, the problem is fixed.
The 'ignore ownership' is persistent.

Reason was
- the Mac did not drive down since long time due to a mounted cloud space of a third party provider (not Apple cloud).

I had to fix this as obviously only with a regular drive down of the Mac OS the HD configuration is being saved.

I deleted the file "volinfo.database" before, however this alone did not work.

thanks for the update!

I have been having this problem, and I was reluctant to follow the advice to remove the volinfo database. Instead, I did an erase + clean install of MacOS (Mojave) and then restored user files. I assumed that since the volinfo.database does not live in my home directory, it would be renewed from scratch when I did a clean reinstall. My assumption turns out to be not correct; after the reinstall and restoration of one user, the file was reconstituted with scores of entries (and, presumably, whatever syntax errors might have accumulated).

I erased the volinfo database, as suggested above, and, at least after one reboot, "Ignore Ownership On This Volume" appears to be sticking to its assigned value for the first time in years.

Thanks SoftRAID Support -- I wish I had followed your advice the first time.

This is an OS X issue with persistance on "ignore ownerships". That is why deleting this database can fix the problem.