Thanks, let me know if I should try bothering along to
@Loki. I have generally pestered him previously, back when the problem was that we couldn't upload new image attachments when editing an existing thread. This issue looks very patchy to me - a couple ".png"s in a thread won't work, while ones further down do. Same issue in Ped's group, from a quick glance.
It makes me wonder if it's related to the previous fix, since I heard there's much duct tape and string involved in getting the permissions to work in the groups (particularly). If the guides section is likely to be significantly more stable and reliable then there may be the odd, bigger post I might put there instead, since I intend quite a few things as general reference resources for casual visitors from Reddit, YouTube, etc. Ta.