Thank you for the bug report, i just created an account to do the same.
Since there is no proper way to reproduce the same color correction on the next raw file with xml or something, because it has exact the same light conditions, I'm using this preset thing workaround. And like calebcudjoe has mentioned, if you have saved a preset, than you will open the next raw file, the preset is already preselected but not applied to the image, you have to click into the preset-dropdown menu, wild clicking another preset or "default" and then re-select the desired preset as before. Affinity Photo 2 will now apply the preset without changing the white balance.
The white balance will not be applied, even the checkbox is on and the saved values are shown. In reality, the white balance of the raw file is still mistakenly active in the background. The workaround is not to deselect the checkbox and reselect it again, I have to change the temperature value, as an example reduce it by 1 from 5115 to 5114 and go back to 5115. After that the white balance will be applied.
It would be great, if this bug gets fixed soon.
I do have one question, could you integrate the function that if you are saving a preset, an checkbox would appear to decide to save not only the basic tab, but also the whole other stuff like: lens, details and tones. Because you will never go to those 4 tabs and reselect the preset, again and again. Because I have raw files, made in the same light conditions, by the same lense, I want the same charpness or noise, the same look. For this, I have to go to all 4 tabs and reselect a preset.
It would be great, thank you!
cheers, konvrgnz