The different block chains is due to the new 0.11 clients starting to enforce the soft-forks from Bitcoin (BIP34, BIP65, etc).

These are enforced if a certain number of blocks are mined on the new wallet.

Since the majority seems to be on the new wallet, I suggest everyone upgrade to the new version to remain compatible.

To get the fork info on the new wallet you can type:

getblockchaininfo


{
"chain" : "main",
"blocks" : 2010486,
"headers" : 2010486,
"bestblockhash" : "00000006a0f46da556779ea27b0ae43054ab294500ea1bfbe5a97871a8c35eed",
"difficulty" : 0.13478134,
"verificationprogress" : 1.00000026,
"chainwork" : "000000000000000000000000000000000000000000000000001dc91cf4f3258c",
"pruned" : false,
"softforks" : [
{
"id" : "bip34",
"version" : 2,
"enforce" : {
"status" : true,
"found" : 8000,
"required" : 750,
"window" : 8000
},
"reject" : {
"status" : true,
"found" : 8000,
"required" : 950,
"window" : 8000
}
},
{
"id" : "bip66",
"version" : 3,
"enforce" : {
"status" : true,
"found" : 8000,
"required" : 750,
"window" : 8000
},
"reject" : {
"status" : true,
"found" : 8000,
"required" : 950,
"window" : 8000
}
},
{
"id" : "bip65",
"version" : 4,
"enforce" : {
"status" : true,
"found" : 8000,
"required" : 750,
"window" : 8000
},
"reject" : {
"status" : true,
"found" : 8000,
"required" : 950,
"window" : 8000
}
}
]
}