Did these sticks come together in ONE kit.
Was the kit clearly unopened or could you tell it had been opened previously?
That's really weird, because, it's not possible. Memory cannot run at two different speeds. When two different speeds are installed it must ALWAYS default to the speed of the lower stick. Something else is going on.
Make sure you have the latest BIOS version for your motherboard installed? If you don't, install it and check again.
My instinctual answer is to tell you to first remove and reinstall the memory. Make sure it is fully seated.
If nothing changes, I would pull the CPU and make certain that there are no bent pins. Weird crap like this is usually the result of something like a bent pin or something being shorted or not fully plugged in somewhere.
Might also be a good idea after you verify you have the latest BIOS, verify there are no bent pins and verify that the RAM is fully seated and there are no foreign objects or debris in any of the DIMM slots, and that the DIMMs are installed in the second and fourth slot over from the CPU socket going left from the CPU towards the edge of the motherboard, that you do a hard reset of the BIOS as follows.
BIOS Hard Reset procedure
Power off the unit, switch the PSU off and unplug the PSU cord from either the wall or the power supply.
Remove the motherboard CMOS battery for five minutes. In some cases it may be necessary to remove the graphics card to access the CMOS battery.
During that five minutes, press the power button on the case for 30 seconds. After the five minutes is up, reinstall the CMOS battery making sure to insert it with the correct side up just as it came out.
If you had to remove the graphics card you can now reinstall it, but remember to reconnect your power cables if there were any attached to it as well as your display cable.
Now, plug the power supply cable back in, switch the PSU back on and power up the system. It should display the POST screen and the options to enter CMOS/BIOS setup. Enter the bios setup program and reconfigure the boot settings for either the Windows boot manager or for legacy systems, the drive your OS is installed on if necessary.
Save settings and exit. If the system will POST and boot then you can move forward from there including going back into the bios and configuring any other custom settings you may need to configure such as Memory XMP profile settings, custom fan profile settings or other specific settings you may have previously had configured that were wiped out by resetting the CMOS.
In some cases it may be necessary when you go into the BIOS after a reset, to load the Optimal default or Default values and then save settings, to actually get the hardware tables to reset in the boot manager.