From another listserve yesterday:

"The MACPA was told by the C’s Deputy Director that they are asking all PTE’s that filed the old 510 trying to make the entity election (instead of waiting for the 511) to “amend” by now filing the 511. Most of those 510s with election are likely wrong. HOWEVER, we were also told that in the expected-to-be rare case that the 510 tax calculation and related information to the members turned out to be exactly the same as what would show on the 511, the new 511 is not needed to be filed. TROUBLE is that there is no way for the C’s office to know whether the filed 510 produced the same calculation and info as a 511, and thus the expectation that the 511s will be filed. There is likelihood that the 510s with election that were processed (in error by C) will be pulled and reviewed and notices sent. So if there is any difference (and to the state, one dollar is a difference), it is best to amend by filing the 511, or else anticipate having to spend time with notices later."

C = Comptroller of Maryland