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DMA and RCC Low Power Enable bits (LPENR)

Question asked by jre.jre on Nov 17, 2016
I'm on an STM32F4 and using an RTOS.  I put the MCU to sleep whenever the scheduler has nothing to do using the WFI instruction.  
I'm using DMA1 with i2S and a USART.  I want to disable the DMA1 clock using the RCC_AHB1LPENR_DMA1LPEN bit which means the clock is disabled when the mcu is asleep.  The problem is that sometimes the UART doesn't function when RCC_AHB1LPENR_DMA1LPEN=0 even though the MCU is awake.  The UART is never able to complete it's transmission.  

Does anyone have any advice on how to use the RCC_AHB1LPENR_DMA1LPEN bit? Resetting it adds about an hour to battery life so I don't want to just leave it set all the time.