So, I first noticed this a few weeks ago in a modded copy of 1.12.3 I have. Essentially, anything I have in orbit has its Pe decrease and its Ap increase, with no discernable reason why. These were basic craft with no RCS at all, and I am absolutely certain the throttle was at 0. So I deleted that save file, made a new one, and tried again. I noticed the problem again. So then I nuked that copy, took my clean steam copy, and replaced it (and reinstalled all my mods). The problem persisted. I nuked the steam copy, and redownloaded it, and waited, then copied it and modded it, and tried again. Still the same issue. On a lark, I just tried playing from the clean copy, and noticed the issue is present, thus ruling out any mod causing it. I revalidated the game files, retried it, and its still acting up.
If there's any specific files I need to include, let me know and I'll provide them.