So let me tell you what happened next :-)
- I have 50 XRP thanks to Azrael.
- I fill the grant trust form for 100 BTC
- The page answers red: you need 50.000000012 XRP to to this. I try to check my balance:  it disconnects me
- I reconnect: it says I only have 49 XRP, and the trust area is blank, saying I need more ripples (it says a hundred would be good...)

So I apologize Azrael, I lost one of the precious XRP you gave me. Maybe can you help a bit more?

Cheers