Editing app_config and cc_config fails on Win10

[Jimbocous]

[posted this a couple months ago at 1/75 beta but no response so reposting]
Just loaded 1.75, and decided to test the new ability of editing app_config.xml.
Setup here is as follows:
1) Core2 Q9650, Win10ProX64, BT 1.75, BOINC 7.8.3, Projects: SETI, Einstein
2) Xeon E5450, Win7ProX64,                   BOINC 7.8.3, Projects: SETI, Einstein
3) Xeon X5675, Win10ProX64,                 BOINC 7.8.3, Projects: SETI, SETI Beta, Einstein
4) Xeon X5675, Win10ProX64,                 BOINC 7.8.3, Projects: SETI, SETI Beta, Einstein
Installation file paths are standard for BOINC and BT on all machines.

From machine 1) under Projects tab was able to load and read app_config for Einstein and SETI Beta on all machines (SETI uses app_info on all).
However, after making a change to Einstein on all 4 machines and to Beta on the two machines running it:
Syntax Check passes,
Apply passes,
A subsequent attempt to load app_config yields an "Invalid" window message in each case.

Further checking shows that each app_config is now file size 0 and all data has been lost.

Stupid me, of course, for not having made backups before testing a new feature, and for not having validated everything on 1 machine before moving on to the other three.
But I thought I would mention this for anyone else testing, to see if there's something else I did to screw this up or info I can provide to help find a resolution.
If I might also suggest, perhaps it would be good to have BT make a .BAK backup file of app/cc_config XML files before making changes to them, if that is possible.
Feel free to let me know how I might help! Thanks!

[edit 1]
It seems app_config editor is failing syntax check on <gpu_versions> statement. 
CC_Config editor is failing syntax check on <cc_config> tag.
Falling back to 1.73.

[edit 2]
Unable to fall back to version 1.66 or 1.73, as running installer gives error:
Open file:C:\Program Files\eFMer\BoincTasks\lang\BoincTasks_ENU.btlang
Group: <GroupMenuMain> string header in pos 225, <ExtraEditAppInfo> not found
Group: <GroupDialogRules> string header in pos 951, <EventSuspendNetwork> not found
Group: <GroupDialogRules> string header in pos 952, <EventResumeNetwork> not found

[fred]

The installer doesn't like to install over a new version.
Normally you have to use the Windows way to remove the program in the control panel.

To revert to the old version delete this folder
C:\Program Files\eFMer\BoincTasks\lang

Delete boinctasks64.exe
Now install again.

[fred]

The Boinc client overwrites the config files and returns a zero file when it fails.
That's a serious flaw in the client nothing I can do, as BoincTasks uses the BOINC client to send the new file.

I know there were a couple of errors in the BOINC client that causes the app app_config.xml to fail.
Was unable to test the end result as I was waiting for the changes to run true the system.

It will be at least a month before I can look into this.

[fred]

Fixed in V 1.77
You need 7.10.2 for the app_info.xml to work.
Writing cc_config.xml changed in BOINC client 7.10.2  that broke all Boinctasks before 1.77.