Make app as default not fully being activated

Expected behavior

I expect that after accepting the prompt and giving it permission to be my default message app, it should be so unless I deactivate it manually and I should have the option of using my other apps normally if need be.

Actual behavior

After accepting the prompt and giving it permission, it resets whenever I open my normal SMS app.

How to reproduce

• Install QKSMS app
• Open and accept prompt
• Grant it permission to be your default message app
• Now, open your normal message app
• Go back and open QKSMS app, it'll now reason for you to set as default message app.

Device

• Operating system: Android 7.0 Nougat
• Device: Xiaomi Redmi Note 4
• Kernel Version: 3.18.31-perf-g021e4fd
• Build version: 3.0.5

Recording Of The Bug