Odd. Even if you had two versions open, only one of them would normally get called to open the downloaded file.
Is it possible you are double-clicking somewhere when only a single click is needed?
Normally if one copy of ADE is running, trying to run another copy will just go to the first one,
but it might be that double clicking can start two so close together the second doesn't notice the first had already started.
Is this opening of two copies of ADE a regular problem now, or did it just happen once?
Do the two copies of ADE that open look the same?
Can you ask in the Help/About to see if they are two copies of the same version, or tow different versions?
Phoning won't be so good as I am in UK.