Use Blackpoint Compensation checkbox in Convert Color Space panel does nothing, the setting needs to be selected in Krita Preferences color panel tab, and blackpoint compensation takes effect on converts after a restart. The checkbox value does not reflect the action being taken. Blackpoint compensation might not be the only setting with this issue, but that's the one I can reliably test.

Reproducible: Always

Steps to Reproduce:
1. Make sure display is calibrated and capable of showing dark greys, using an ICC profile
2. Create or find an image with very dark greys (1-10%) on a black background
3. Disable blackpoint compensation in Krita Preferences, restart Krita if a change was made.
4. Make a conversion using Image -> Convert Image Color Space... that results in black crush, in my case from RGB 8 bit sRGB-elle-v2-srgbtrc.icc (default) to 16 bit sRGB-elle-v2-g10.icc (default)
5. Undo, then make the same conversion but with the checkbox for Use Blackpoint Compensation enabled

Actual Results:  
The dark greys get crushed to black

Expected Results:  
The image should remain visibly unchanged between conversions.

Version I have is http://files.kde.org/krita/windows/krita_x64_2.9.6.3.msi on Windows 10. I am using this ICC profile, which results in visibly brightened darks on my monitor when applied http://www.tftcentral.co.uk/icc_profiles/asus_pb278q.icc and this PNG file as a test image http://www.lagom.nl/lcd-test/img/blacktest.png