Emails from Inbox getting moved to Trash (not by me)

[yehwhatevr]

I have noticed over the last couple of weeks, several instances where messages were automatically moved from the inbox to the trash. This happened after I read a message (went back later to respond and it was gone) found it in the trash... and again (separately) I read a message, hit reply (immediately) sent the response then found the original inbox message in the trash.  Anyone else experiencing this or have any suggestions as to what could be causing it?  I checked the settings, but they seem to be very limited (as far as what I can see/change etc..)