The MSPFR4xxx_FR2xxx Family User Guide ( SLAU445G ) documents CSCTL4 bit 9 as read-only Bit.
The "MSP430FR2xx_4xx" DriverLib´s cs.c implementation of CS_initClockSignal clearly write 1 into it if called with CS_ACLK, CS_VLOCLK_SELECT.
In addition to this: it doens clear the Bit if called with one of the other sources since " &= ~(SELA);" only masks CSCTL4 bit 8.
So: Does this chip family actually support CSCTL4 Bit 9 or is this just an undiscovered Bug in the DriverLib?