What platform (Mac/Windows) and version (11.1x/12.0x/13.0x ...) are you using? Which models are causing problems?
I've seen this problem in version 12.0b, and it was fixed in 12.0c (for Windows)
In case you aren't aware of it, the people at Hash are fixing problems and releasing new versions very frequently. It's always a good idea to download and install the latest update for your version of A:M.
For v11.1 and earlier you need to go to the Hash FTP to find the latest version:
ftp://ftp.hashmirror.com/pub/updates/
For v12.0 and v13.0 there is a forum where WillP announces new version as they become available:
http://www.hash.com/forums/index.php?showforum=2
The latest version of v12.0, v+, should not have these problems as it's well tested by now. V13 on the other hand is quite new, so if you already have the latest version and still get the problem you should file a bug report in the A:M Reports: http://www.hash.com/reports/main_page.php