Sometimes when you edit the build.prop and restart your phone, the changes you have made in the build.prop are gone.
This zip must be flashed through recovery, custom recovery of course.
After flashing this, your apps will be able to read/write on external memory. Apps like Titanium Backup for example, or any app that needs to read/write the external memory of the device.
For example in Titanium Backup you can set your external memory as the default storage for backups, this way saving some internal memory.
Put the zip on your sdcard
Go to recovery
Click on KitKat Write to ext_sd FIX
Swipe to confirm Flash
These instructions are for TWRP recovery, but in CWM it's pretty much the same.
Thanks to @TEKHD for making this for SAMSUNG devices.
I just ported this to HTC and modified the platform.xml
Should work on both stock and custom rooted ROM's.
NO S-OFF required.
I am not responsible for any damage to your device while installing this, proceed at your own risk.
This zip was tested on a HTC ONE M8 device.
Dev-Host Download link
KitKat Write to ext_sd FIX