DukeLeto7 No, I meant the sword in the upper left room (guarded by stationary unit), not one of the two hidden chests in the lower right room.
When I first played the game (it was version 0.58.3 RTP) I took long time to wander in the mansion before going to Megail (and also some time to wander before this section), then I defeated almost all enemies except for the stationary guard and the boss, and only when I opened the chest. I received either claws or leather armor (don't remeber exactly which item it was) but not the shinig sword. I reloaded saves in the mansion several times, but still got only one sword from the hidden chest. Only after I loaded from before Revan's compaund and stormed through everything until the end, I had got two shining swords from the manor. That's why I assumed that there is maybe a hidden timer for this section.
I think I still have a save directly after the manor, but I don't have close prior and as I said I wasn't able to replicate this in the version 59.
P.S. Just for the record I didn't use any save modifiers.