Yes, that is a true statement, if you have found a solution, it should be posted, like Sgadan Ruadh has done.
Meanwhile we are good friends and sending us emails almost every day.
Ok, back to your last question.
How/Where do you see that there 890MB left?
Are you using photo stream?
There is iExplorer from Macroplant for the Mac. You can perhaps use it to explore your iOS devices.
I am not using photo stream or any other cloud services for photos.
If I go to settings, general, usage, then I can see 890MB being used by PHotos & Camera. If I touch that, I can see camera roll using 585mb, and photo stream using 305mb. That makes no sense, I have only 3 pictures in the camera roll.
I am using iTunes to sync photos from a PC with Windows 7 to an iPad 4 with IOS 8.1.3 and an iPhone 4S with IOS 7.1.1. There are 102 photos in a single folder on the PC. Only 92 will sync on both Apple devices using iTunes. It is the same 10 photos which do not sync on both iPad and IPhone. I have uninstalled and reinstalled iTunes and deleted the iPod Photo Cache but to no effect. I have read through some (but not all!) of the above posts but cannot see a solution. Thoughts and/or links to other relevant threads would be welcome.