Well, that points system - at least in my specific case - is rather meaningless metrics, it doesn't reflect my knowledge/experience, it rather means that I am a prolific poster with a friendly attitude.
I mis-read your model as CRS, and I can imagine a few possible settings that may cause the issue you are having on RouterOS, but on SwOS I have no ideas.
The usual recommendation is to not use special characters, see point #29 here:
GP & CSA for Mikrotik devices
outside of the ASCII 7 bit set, because of possible different character encoding, so "%" should be fine.
So, if the issue is not on the browser side (cache, strange auto-save something, etc.) logically it can only be some kind of corruption of the device storage.
This - due to the way flash is organized - could be a rare "bad sector" that was not mapped as such when the OS was deployed or one of those intermittent failures that populate the worst nightmares of electric and electronic engineers attempting to troubleshoot one of these issues.
Your device is (should be) a recently bought one, personally I would - once you get the replacement - RMA it, if it is possible under warranty.
Even if with a reset you re-gain access to it you cannot be sure that the issue would not represent itself (if the issue is with storage).