Hi there.
In case I don't get an answer you can view this as a bug report.
I have an Exchange 2013 CU8 on 2012R2 with all updates applied, no hotfixes. It's a brand new install. It's a VM running on a dedicated RAID1 array of 2 SSDs on a new Dell R720xd.
If I try to import more than 2 PST files at one time they fail and start over again in one big loop even though, it would appear the import was 100% complete.
PSTs were imported form a folder with SMB and NTFS rights that allow for exchange trusted subsystem. User account obviously has role rights to import as it works fine when only 2 jobs are submitted.
You can see below what happens with 3 jobs running. This repeats over and over, each job bombs out at a random percentage with error relinquishedwlmstall.
-=Chris