When using the teleporter to transfer between dimensions, my xp bar temporarily dissapears. The xp isn't lost but as far as enchanting tables and other items that use xp, I might as well be a fresh lvl 0. Relogging or killing something causes the xp to come back to where it was. At first i thought it was something to do with RFtools dimensions, but it even happened when teleporting to the nether. Pics below show what happens.

--Before using the portal to the nether--

-- After arriving at the nether, xp is gone--

-- after using a bottle of enchanting my xp is back --

Not just a Mekanism issue. I've seen it with at least two other teleport-type mods. Now I'm trying to remember if the vanilla nether portal does it too...going to have to satisfy my curiosity tonight.

i watched lately some modsauce2 videos from xBCrafted (hermitcrafter) on youtube and he has the same problem using some other portals mod

This bug used to happen in Galacticraft, but between dimensions, no teleporter involved: micdoodle8/Galacticraft#1336

This is simply a client desync problem, doing anything that causes the server to force the client to update (e.g. using a Bottle 'O Enchanting) causes the GUI to update.