Compatibility issues, changed toolset from "Cross ARM GNU C" to "MCU GCC"
Happily today nothings makes me sad anymore about the MCU GCC options.
In fact the faulty behaviour was due to mixed up content in source files.
Tx for response. According to the response it looks like the MCU GCC is the better choice for STMF4 or STM uCs at all due to proper setting options.