I looked at the pictures again and maybe there is a difference. I am using a OTG miniB to USB connector and not a standard cable with a F-F adapter. It works fine with the USB flash drive however...
Is there a difference between the two ways of connecting it?
Here's my connector: I'll have to get the picture later as it looks like the company's web site is down (or they went out of business because the connector doesn't work ;-) )

C