This was previously reported but is still existant in the latest PTS patch. Therefore, I thought it would be good to write a thorough report on the issue and provide some examples, with screenshots, of the various behaviours that are problematic.
Currently, thieves troves are programmed identically to chests: you can crouch, but the moment you interact with them and fully open, you become exposed/detected, unlike safe boxes, which allow you to remain crouched unless someone gets into detection range. This has the effect of causing all interactions with thieves troves to be detectable by anyone nearby. This behaviour seems sufficient for chests, as these are not criminal activities, but unsuited for thieving.
While the majority of troves themselves are actually hidden, there are quite a few that I have run across on PTS that aren't.
1. Bleakrock Docks: this trove in the bottom of the boat is impossible to loot during the initial phase of Bleakrock, with a large number of NPCs present. As the screenshot demonstrates, although I am crouching and was successfully crouched up until opening the trove, I received a bounty when doing so. Removing the items gives additional bounty.
2. In a hut in Dhalmora, Bal Foyen: The angle on this one is difficult to demonstrate, but the NPC has its back turned to you and the trove, allowing you to stealth:
Upon opening the trove however, in the identical position, you are detected and recieve a bounty:
As far as I can tell, having sat here for a number of minutes, the NPC doesns't move, meaning that, like the Bleakrock Docks, the trove is an unavoidable bounty.
I believe there is another location in Wrothgar near the Narsis Dren quest-chain barrow that is similarly near NPCs that cannot be opened without accruing a bounty. However, my pre-made toon on PTS doesns't have access to that area currently.
1. Relocate troves near stationary NPCs so that players can safely access them.
2. (Ideal) Use safebox programming so that players can remain stealthed while opening troves, unless an NPC comes too close, etc. This would make them function as expected.