attachInterruptWakeup firstly fires instanly, then goes normal

[pushkin42]

Have a next situation:

• BI = PA0
• STM32F103C8T6 (hand-made board)
• PlatformIO IDE

 LowPower.begin();
 LowPower.attachInterruptWakeup(BI, _INT0, FALLING, SHUTDOWN_MODE);
 LowPower.shutdown(0);

_INT0 is a function that simply sets flag.

My device goes shutdown and instantly reboots (power up again) after first shutdown. If I left power connected, two and over "shutdown" are normal - wakeup on PA0 as intended. If I remove power, wait for a while, connect power - device shutdowns and reboots after timeout instantly. Then, shutdown mode works fine (10 seconds after last FALLING edge on PA0).

PA0 connected to buttons that connected to gnd + pullup to VCC with 10kOhm resistors and capacitor 0.1uF