We discovered this while debugging code that involves concatenating two ints and using the result as a long key in the TLongIntHashMap. This was also reproducible in the TLongIntIntHashMap and TLongIntObjectHashMap.
4294967297 is the result of the expression (((long)1 << 32) | 1)
Using multiples of this number for keys results in significant slow-downs.j
Attached is a small java program which demonstrates the issue.