Just click Save Changes without changing anything. Works for me now. Possible this was because this is such an old bug report? Or you accidently tried to move the bug.
€: They real questions is why do you want to subscribe to such an old bug report?
Thanks, @Duha – works for me too now, since the GUI doesn’t appear anymore. I can only imagine that an attribute was invalid, and thus it requested support from whoever next interacted.
I am no expert on bug reporting/triaging, but my understanding is that for very old fixed bugs you should create a new bug report, even if it appears to be the same issue.
Therefore its probably not worth to subscribe to old fixed bugs.
An exception would of course be FRs though, right, @Duha? After all, engagement with those is probably the sole method of interest now that Voting is unavailable at https://bugs.kde.org.
Sorry I don’t know what FRs is.
€: Feature requests?
I didn’t want to imply that CC’ing to open Bug reports or Feature requests is useless. Just those that are long closed.
It is just that this bug report was closed years ago. So I don’t know how CC’ing would be useful unless you reopen or create a new report.