Sorry for coming late to the party....
Too bad that you are experiencing troubles with mbf.
I have been mostly working on mbf-freertos in the last time as this is (for me personally) the way to go in the future.
I started using the git-wiki for fpc-freertos and based on your comment it looks like it makes sense to do the same thing for mbf.
Please let me go through mbf with bluepill in mind, I will provide a new version later today based on what i find, i already found one or two places that could be done better for that special chip.
Please also note that mbf for bluepill is curently only good for gpio, uart and spi, i2c does not work for stm32f1, but it is something that can be implemented, I just never needed it and it was never asked for.
Michael