DB with -directio leaves file handles open in Connect&Disconnect cycle after ADDONLINE

After adding extents online (addonline) client sessions eventually fail to open a connection to the database having exhausted filehandles
Clients are unable to open a connection to the database as all system file handles had been allocated
Client session connection fails with error 43 errno 24: Too many open files
File handles are exhausted (ulimit -n)

Database extents were added online: prostrct addonline.
Database started with -directio startup parameter which uses Unbuffered Synchronous I/O (O_RDWR|O_DSYNC) 

Strace of the client session shows the added extent(s) are opened with two file handles:
Strace of the client session shows older extents are opened with on file handle:

Without directio file handles are properly closed on client disconnect.
After database shutdown and restart with -directio, file handles are closed on client disconnect as they should be.
errno 24: Too many open files

New connections opens double amount of file handles after prostrct addonline.

• Older extents are opened with with “UNBUFIO” once == O_RDWR|O_DSYNC
• Newly added extents are opened with “BOTHIO” which results 2 file handles, one for “BUFIO”, one for “UNBUFIO”

Upgrade to OpenEdge 12.2 where PROSTRCT addonline sets the mode for newly added extents as "UNBUFIO"

When using the -directio database startup parameter, schedule downtime to add extents to the database.

Progress Article:

 Does Progress use Synchronous or Asynchronous I/O?