Setting table_definition_cache to -1 causes the server to run out of memory

I noticed that when I set to -1 (auto-tune), the server memory kept increasing till the server ran out of memory and mariadb was killed by the OOM tracker. When looking at the server before this happened the next time, I noted that the table_definition_cache was already at 2097152. When I set the table definition cache back to a small static number (2000), ton's of memory was freed and since, the system has been pretty stable.