trigger using logseverity not always working

[nth]

Hello,

I have an active item collecting some memory and disk related events from the Windows event log. I tried setting up a trigger for this as well, to report anything above 'Information':

{template_av_windows:eventlog[System,@mem_or_disk].logseverity(0)}>1

But this produced no alerts when it should have (I could clearly see the entry logged in 'Latest data', having 'Warning' as severity). So I then changed the trigger to:

{template_av_windows:eventlog[System,@mem_or_disk].logseverity(0)}=2 | {template_av_windows:eventlog[System,@mem_or_disk].logseverity(0)}=4

And now alerts started coming in. Any ideas why the first trigger isn't... triggering?

LE: I forgot to mention - Server and agent are both 1.8.3.