Decimal precision intermittently resets between cell executions

Hi, I had opened a Jupyter issue on this, but it sounds like this is a better place for it.

In short:
Setting decimal precision via `decimal.getcontext().prec = x` intermittently fails to retain the precision setting between cell executions, often resetting decimal precision to 28.

More detail in the original issue:
https://github.com/jupyter/notebook/issues/5260

Let me know if you need any other details - thanks!