yup, this also happened with my female mesmer. i chose not to post in the other forum because it had all ritualist posts...and this was not ritualist related.
this happened about 14 hours ago. i logged into my mesmer to put some tomes on her, and i thought it was slow loading---but it turned out this invisibility lasted like 2 hours until i logged off---and still has problems to this very minute.
i did participate in the weekend gwen event, but did not take my mesmer over, just my necro and ele. so she has not been in the HoM, or for that matter has no gwen items on her whatsoever.
i have primeval armor from nightfall dyed black--and people were describing my armor as "is this norn, llyodia?" and "wow you are frightening---what happened to your body?" and others exclaimed "i cannot see you!!!" well, gee, neither could i...until i took the armor off, but when i put it back on, it did show back up, but not in the inventory window at all, and was missing major parts of the armor
i need to see my fur! MY FUR!
i am not able to link any attachments, as i am experiencing technical difficulties (with i think my firewall

), but i do have 2 screenshots that are similar in nature to the ritualist page: one with invisible character and name/title under it, and the other shows that the primeval armor is missing parts, especially on the "chest" piece.