I know that 3.26 was supposed to fix a problem with settings being erased when upgrading to 3.25 but I did have that problem when upgrading an rb-333 that was at 3.25 to 3.26.
It was one board out of 50 but it was an important access point.
I lost wireless contact after the upgrade and had to drive 10 miles to connect via ethernet.
The settings for the wireless interfaces ,1 XR5 and 1 XR2 where completly gone.
The Bridge was gone but the routes and ip address remained although the address assignments had been jumbled across the interfaces and no longer worked.
After entering the correct settings the system has worked fine and it does report that it is at 3.26.
I did not have this problem with the upgrade to 3.25 anywhere in my network.
The question becomes as we have now moved to 3.27 is the issue in 3.25 that caused the losss of settings still here ?
the problem was in the v3.25 itself, it could mark some important NAND sectors as bad. you must make a backup file and save it off-site before upgrading. I’m sorry, but there was no easier fix.
Well I dodged a bullet then.
I have upgraded eveything from 3.26 to 3.27 in the traditonal way.
Do you think that my systems will be stable as I didn’t save the settings off site ?
I would assume if I was going to have a problem it would have shown up by now.
Perhaps the fact that the configurations existed in the 3.26 enviroment I have copied the memory leak issue into 3.27.
What do you think?
no, you couldn’t copy the bug over to the next version 
everything should be fine now, if you have v3.27