shortly:
messages having the same timestamp in the same logstore should be returned by the log-manager methods in the stored order.

It for sure affects tpl_log_manager_get_filtered_messages(), maybe other methods.

explanation:
log-manager sometimes sort logentries, this because it queries multiple logstores and then merges entries together before returning.

When entries have the same timestamp (granularity is second, so it is possible to happen), they are returned reversed respect the stored order.

Example:

in logstore those messages are stored in this order (format = timestamp + text):
time='20100226T12:39:03' 1
time='20100226T12:39:04' 2
time='20100226T12:39:04' 3
time='20100226T12:39:05' 4
time='20100226T12:39:05' 5
time='20100226T12:39:05' 6

if tpl_log_manager_get_filtered_messages() is used getting the last 5 lines (as empathy does), the result will be:

3
2
6
5
4

which means that the methods sorts '2','3' (TS1=12:39:03) and '4', '5','6' (TS1=12:39:04), returning them in reverse order within the group, but sorted correctly chronologically (TS1<TS2)

I'd expect, because of the storing order:
2
3
4
5
6

"time='20100226T12:39:03' 1" is correctly skipped since I wanted only the last 5 messages.