calcLpTokenSupply is used to calculate the lpTokenSupply for given reserves. We found some values for reserves (with large ratio difference), or very small reserves, which result in impossibility to converge and repeatedly calculating the same lpTokenSupply. 
Issue 1:
For large ratio reserves - one such reserves are:
Issue 2:
For very small reserve amounts the same issue also arises - it only happens with the new code:
Testcase for Issue 2:
We didnt manage to identify a solution to this problem, but the behaviour can be documented with a @dev tag.
