Two Linux boxes, each plugged in via Ethernet to a BATMAN node (two nodes). The nodes talk batman-advanced to each other via WiFi. The Linux boxes can ping each other all day long. Both Linux boxes have Apache running. Downloading a file via HTTP works only if the file is smaller than or equal to exactly 1,145 bytes. TFTP file transfers are halting, but they get through (4 megabytes took a couple of minutes).
This happens with both r1176 and r1298 on OpenWrt.