Running (for example):
$image->Set(Alpha=>'Set');
does what it says on the tin !
For those of us with thick fingers, running:
$image->Set(Alphs=>'Set');
also runs (at least on my system), but creates an "Alphs" tag within the $image file with the value of 'Set'. This appears to happen silently (i.e. no warnings or errors).
The erroneous "Alphs" tag can be found using $image->Identify(); under Properties.
Whilst the ability to embed you own custom tags is certainly handy, it's a bit of a pain when it comes to troubleshooting!
I've not checked to see if there is the facility within perl magic to trap this error (I'm a bit lazy when it comes to error trapping in my scripts).
Hopefully this will save somebody some time at some time.
Mike