After applying a theme with CaptionBarHeight set, caption height from SPI_GETNONCLIENTMETRICS is set
to the specified size. However in refresh_sysparams(), the caption height is refreshed and the value
from SM_CXSIZE is used and ends up overwriting the theme specified caption height. SM_CYSIZE is the
correct index instead of SM_CXSIZE.

You may need to turn a theme off and on for the correct caption height to take effect after the fix.