I'm not surprised about the general scrutiny of volunteer visas now, but they basically made it impossible for anyone who has had one previously, to get a new one.
The certification they are asking for is brand new information for everybody I have spoken to, and is only obtainable from within Thailand..
Also, asking for my previous paperwork from extension (which is taken by the immigration office on application) seemed to be a spurious attempt to make it virtually impossible to apply anyway.
Back to back volunteer visas are pretty much a no-go now.. at Vientiane anyway.