After a series of residues (1+) with alternate conformations, the H atom of the next residue seems to lock its occupancy to that of the final conformation of the previous residue. Hence I'm getting several H's with 0.1-0.5 occupancy on single conformation residues, where the entire rest of the residue has occupancy 1. This happens after every altconf series, and showed up in two separate structures I've worked on this week. Within a series of 2+ residues with altconfs, the H's refine correctly with their altconf groups. So it isn't just that all subsequent residue's H's are getting overridden. This behavior seems to have started with 1.8.1-1168, or at least previous refinements of the same structure didn't do this. 64 bit build on Retina MBP running OS X 10.8.2. I couldn't google any reference to this behavior, so assuming it's a new bug I can send along source files. Below I've pasted a couple residues from one of my PDBs. I added a ***** to mark the offending H with the wrong occupancy. -Alex Scouras ATOM 668 N CMET A 29 -17.970 6.464 59.720 0.21 10.72 N ANISOU 668 N CMET A 29 1641 1300 1133 -328 -379 -50 N ATOM 669 CA CMET A 29 -17.578 5.189 60.316 0.21 9.05 C ANISOU 669 CA CMET A 29 1545 882 1012 -248 -350 -140 C ATOM 670 C CMET A 29 -17.248 5.317 61.797 0.21 7.83 C ANISOU 670 C CMET A 29 1363 666 947 173 -134 166 C ATOM 671 O CMET A 29 -17.496 4.395 62.578 0.21 7.92 O ANISOU 671 O CMET A 29 1187 751 1071 371 -145 338 O ATOM 672 CB CMET A 29 -16.376 4.609 59.573 0.21 9.09 C ANISOU 672 CB CMET A 29 1561 834 1059 -243 -283 -203 C ATOM 673 CG CMET A 29 -16.681 4.210 58.145 0.21 9.05 C ANISOU 673 CG CMET A 29 1529 756 1154 -28 -331 -235 C ATOM 674 SD CMET A 29 -18.049 3.042 58.009 0.21 13.05 S ANISOU 674 SD CMET A 29 2356 1325 1279 -218 -284 -50 S ATOM 675 CE CMET A 29 -17.505 1.757 59.124 0.21 12.06 C ANISOU 675 CE CMET A 29 1866 1485 1232 -630 -667 420 C ATOM 676 H CMET A 29 -17.333 6.878 59.318 0.21 12.87 H ATOM 677 HA CMET A 29 -18.320 4.557 60.216 0.21 10.86 H ATOM 678 HB2CMET A 29 -15.671 5.275 59.551 0.21 10.91 H ATOM 679 HB3CMET A 29 -16.069 3.819 60.044 0.21 10.91 H ATOM 680 HG2CMET A 29 -16.916 5.004 57.640 0.21 10.86 H ATOM 681 HG3CMET A 29 -15.894 3.794 57.761 0.21 10.86 H ATOM 682 HE1CMET A 29 -18.164 1.059 59.140 0.21 14.48 H ATOM 683 HE2CMET A 29 -16.666 1.409 58.813 0.21 14.48 H ATOM 684 HE3CMET A 29 -17.401 2.130 60.002 0.21 14.48 H ATOM 685 N MET A 30 -16.667 6.445 62.187 1.00 6.77 N ANISOU 685 N MET A 30 1361 564 647 -30 -56 18 N ATOM 686 CA MET A 30 -16.416 6.699 63.606 1.00 7.66 C ANISOU 686 CA MET A 30 1362 946 601 -42 -173 2 C ATOM 687 C MET A 30 -17.759 6.724 64.367 1.00 7.62 C ANISOU 687 C MET A 30 1310 944 641 -9 -24 -22 C ATOM 688 O MET A 30 -17.852 6.212 65.486 1.00 9.05 O ANISOU 688 O MET A 30 1571 1151 718 84 98 231 O ATOM 689 CB MET A 30 -15.620 7.987 63.790 1.00 7.65 C ANISOU 689 CB MET A 30 1299 894 714 26 -120 -166 C ATOM 690 CG MET A 30 -14.229 7.965 63.231 1.00 8.62 C ANISOU 690 CG MET A 30 1464 1072 741 31 -163 -10 C ATOM 691 SD MET A 30 -13.130 6.745 64.006 1.00 9.04 S ANISOU 691 SD MET A 30 1555 961 919 105 -180 -94 S ATOM 692 CE MET A 30 -12.812 7.527 65.563 1.00 9.77 C ANISOU 692 CE MET A 30 1540 1284 889 150 -190 -62 C ATOM 693 H MET A 30 -16.395 7.062 61.653 0.21 8.12 H ***** ATOM 694 HA MET A 30 -15.872 5.965 63.962 1.00 9.19 H ATOM 695 HB2 MET A 30 -16.099 8.709 63.352 1.00 9.18 H ATOM 696 HB3 MET A 30 -15.550 8.173 64.739 1.00 9.18 H ATOM 697 HG2 MET A 30 -14.278 7.758 62.284 1.00 10.35 H ATOM 698 HG3 MET A 30 -13.831 8.840 63.354 1.00 10.35 H ATOM 699 HE1 MET A 30 -12.228 6.968 66.079 1.00 11.73 H ATOM 700 HE2 MET A 30 -12.397 8.378 65.406 1.00 11.73 H ATOM 701 HE3 MET A 30 -13.644 7.648 66.026 1.00 11.73 H