[BC660K] QFOTADL reboots even though the delta is invalid

I am doing some tests on corner cases related to the QFOTADL.
There is one situation that does not follow what is specified in the DFOTA Application Note.

The case where the delta is wrong, it should report the error:

+QIND: "FOTA","END",<upgrade_result>

Where <upgrade_result> can be of two values:

0  - Upgraded successfully
255 - Delta firmware package invalid

Here are the logs executing the QFOTADL with the file dfota_diff which is a txt file with dummy content:

cat dfota_diff 
asdjkashdjkashdjkashdjkashdjkahskdasjkdhaskdaskhdak

And the upgrade logs, we can see that the file is downloaded, the module starts the upgrade, and does not report any error. What I would expect is that the command should fail, reporting the proper error, and DO NOT reboot the module.

AT+QFOTADL="http://xxx.yyy.www.zzz:xxx/dfota_diff"
OK
+QIND: "FOTA","HTTPSTART"
+QIND: "FOTA","DOWNLOADING",100%
+QIND: "FOTA","HTTPEND",0
+QIND: "FOTA","START"

# [ module then reboots ]

READY

YES,YOU ARE GREAT;thank for your sharing;