Combi hatch water ingress

Hi,

We had a bit of rain over the last few days around here (roads flooded etc) but when I closed the hatch on the combi, this morning, I heard an unusual sloshing sound.

Tipping the hatch to a certain angle allowed water to, well, somewhere between pour and drip out of the lock latch, which I did until it emptied.

There's a little rubber bung just next to the latch, which I guess should allow water out but, when I tried to see if it was clear, it disappeared inside the hatch.

Is this a common problem? Anything I should be doing to prevent it? 

Thanks in advance.