Lpuart in deepSleep Mode

Hello
I have problem with running NUCLEO-L073 LPUART in stop mode
LPUART can work in deep sleep mode with LSE clock source in stm32l0 series but in Mbed OS serial port driver when you enabled serial rx CallBack function with SerialBase::attach
function it disable deep sleep mode (Line 100 of SerialBase.cpp File)
Anyone can help me?