Default [Q] PAC 4.4.3 rom OTG unmount issue

am on PAC rom 4.4.3
I bought a sandisk dual drive otg 64gb
when i connect it to the phone there is no notification about it but it gets mounted
so no problem there

but the real problem is when i try to unmount it
it says that the unmounting is in process but does not unmount the usb

btw the usb is formatted on FAT32 file system
also stick mount and otg helper apps from play dont work
any solutions??
for device configs see my sig

Phone: Samsung Galaxy SII i9100
ROM: PAC 4.4.3
Kernel: Stock
Recovery: CWM based v6.0.4.8
Modem: I9100XXLS9