Previously you could get around this by overshooting and then editing the clip down, HOWEVER now the edit brings up the original edit interface which does allow you to extend a clip easier BUT also means that the inaccurate timestamp issue is now unavoidable. If this doesn't get addressed I will need to cut Twitch out of my process and just use YouTube's tools or other third party tools.

The clip editor is very inaccurate, as a streamer & content creator I spend time and effort 'cutting' clips perfectly and then the start and end points are different to what I set. It's infuriating!

I'd like to see some more creative options too with clip editing such as mid cuts and maybe some more flexibility in framing the verticals!

ISTG, I thought clipping it without the extra milliseconds and just exact time will do it (ex. 12.5 must be 12.0 so it will not trim the extra milliseconds) and maybe a skill issue on my part but nooooo I just found this thread and a reddit post (a recent one at that too) that it's an actual bug on Twitch's side like WTEF!? Please resolve this!

Please fix this Twitch, it is super annoying & upsetting. Thankyou!

+1 from me.
It's very frustrating when putting effort in cutting clips and the bug happens. some clips likewise need precision in the section of milliseconds. In case of that you've to correct it a few times to get what you would like to obtain. In this process sometimes the clip gets totally unusable because the cut-out milliseconds cannot be recovered after saving. Very annoying if the stream wasn't saved, leaving the "chat team" with no way to create the desired clip.
But well small workaround is to click a few times on the clip-it-button to create some backups for streams without VODs, in case the bug strikes again.
Please let the clip creator be very precise. Thanks!

Significant community on Reddit with the same complaint:

https://www.reddit.com/r/Twitch/comments/1odctxo/clip_timing_not_saving_correctly/