Here's a patch for keeping the temporary indent.
Anton
--- m_old.tmac 2011-02-27 18:19:22.734375000 +0300
+++ m.tmac 2011-02-27 18:23:54.718750000 +0300
@@ -741,12 +741,18 @@
..
.\" Wrapper to cancel the side effect of .tag + .br generating
.\" unwanted vertical space.
-.de misc@tag
+.de misc@tag
+.\" Retain the temporary indent:
+.if !(\\n[.in]-\\n[.i]=0) .nr misc*ti \\n[.in]
.vpt 0
.DEVTAG-\\$1 \\$2
.br
.sp -1
.vpt 1
+.if r misc*ti \{
+. ti \\n[misc*ti]u
+. rr misc*ti
+. \}
..
.\" ######## module pict #################
.nr pict*width 0
