Invesco Mortgage Capital (NYSE:IVR) stock rides up 17%, touching its highest level in almost a year, as retail traders chatter on social media about the mortgage REIT.With short interest at ~13%, some posts suggest the stock could be a short-squeeze candidate.Some 62M shares changed hands before midday New York time, more than 8 times its three-month average daily volume.A couple other mREITs also make significant gains — Western Asset Management (NYSE:WMC) climbs 5.0%, MFA Financial (NYSE:MFA) +3.5%, and New York Mortgage Trust (NASDAQ:NYMT) +2.3%.See IVR's jump in today's trading vs. MFA, WMC, and NYMT as well as SPY in the chart below.SA contributor Harrison Schwartz warns that mREITs like IVR may see a round of rapid margin calls if the Fed starts tapering asset purchases.