STM32F0xx_256.FLM flash algo in Keil.STM32F0xx_DFP.2.0.0.pack specifies page size of 1024 bytes, but according to STMicro RM0091 (see page 56 DocID018940 Rev 9) the page size is 2048k for STM32F07x and STM32F09x devices.
This causes very weird issues in e.g. pyOCD https://github.com/mbedmicro/pyOCD/issues/708
I'm not sure where to report this (obvious?) bug.
ok, sent E-Mail. Will report back here with results for future reference.