WLSE doesn't seem to notice it when an Aironet device goes down

WLSE type: 1105, version 2.7
Aironet 1100 devices (267 pieces), IOS 12.2(13)JA4
After the upgrade from version 2.6 to 2.7 we have a problem with the WLSE. Device discoveries and inventories run without a problem, but whenever a device goes down the WLSE doesn't seem to notice.
With a sniffer we found the WLSE's polling the device, but there's no follow-up when there's no reply. As a result the device stays green.
All configurations are the same with the exeption of one location. Here we've configured the WDS and this is the only location on which the WLSE reacts in the correct way.
On several other locations there might be one or two devices on which the WLSE reacts correctly, but these are exeptions. We have compared configuration files, but can't find any differences between the devices.
Whenever the WLSE does discover a failing device (with no WDS configured) it generates a P1 severity fault (default was P2).
In case these devices have become reachable again the P1 severity fault is automatically acknowledged and remains this way. So far I haven't been able to clear these faults and therefor the device will keep it's alert status in the reportview.
I do hope somebody has some idea about what's going on.
After I encountered these problems after the upgrade I've started from scratch and used a clean installation of version 2.7. and a new discovery of our network.
I really don't know what went wrong. Anybody with any suggestions is very welcome to vent them.
Thanks for your help,

I'm having a similar issue. 500+ AP1200 units, IOS 15JA, newest WLSE version. Most of the time when a unit goes down, it will generate a SNMP unreachable fault message, and we are set to have the WLSE send an email in the event of a SNMP unreachable. That's great. Except once in awhile, it won't generate the fault. The device could be powered completely down for three or four days, and I'd never get a fault message. It's driving me nuts. All these AP's are configured the same using the exact same template, with only the IP info changed.