Positioning problem when logging out in minecart

On the server we have a rail system with button powered booster-rails as start/end points. Sometimes it occurs, that when logged out in a minecart standing on a non-powered booster and you login, you fell down one Block. In Environments, where there is just one Block beneath the rail, you fall through . In cases, where the ground is more solid (more layers of Blocks) you get stuck in the block under it. Resulting in death, when not in OP mode.