Currently running OSX 10.9.1.
When selecting ‘SapmSieve-Train as spam’ in the menu there is a pronounced delay until the e-mail selected is marked and moved to the designated spam folder.
In previous versions, this would be near instantaneous. Now there’s at least a 2-5 second delay. Additionally, if I select the ‘train as spam’, expect it to be trained, then go and select another message, the delay is so long at times that the spam message won’t be trained but the more recent selected message will be ‘trained’.
There’s more about that issue in this thread. The summary is that there’s a bug in Mac OS X 10.9 that causes this slowness, and you can work around most of the slowness using the AppleMailTrainSpamGUIScriptingesoteric preference. I’m also working on more improvements to make it even faster.
You should avoid changing the selection until after the first batch of messages is trained.