During a limited EOE game I activated Uthros for mana and as I went to use the mana the client ended my 1st main phase and took me direct to combat phase. This happened two turns in a row and had to use full control on the subsequent turn to ensure I could spend my mana.

In a previous game I am sure that I had used Uthros without issues, so the issue may have been caused by the board state, unfortunately my attempt to take a snap shot failed, sorry.