--- a/hgext3rd/evolve/__init__.py	Fri Jul 14 02:42:33 2017 +0200
+++ b/hgext3rd/evolve/__init__.py	Fri Jul 14 02:46:28 2017 +0200
@@ -1979,6 +1979,14 @@
 
 shorttemplate = "[{label('evolve.rev', rev)}] {desc|firstline}\n"
 
+def _gettopic(ctx):
+    """handle topic fetching with or without the extension"""
+    return getattr(ctx, 'topic', lambda: '')()
+
+def _gettopicidx(ctx):
+    """handle topic fetching with or without the extension"""
+    return getattr(ctx, 'topicidx', lambda: None)()
+
 def _getcurrenttopic(repo):
     return getattr(repo, 'currenttopic', '')
 
@@ -2012,7 +2020,9 @@
     p1 = wkctx.parents()[0]
     parents = p1.parents()
     currenttopic = _getcurrenttopic(repo)
-    if currenttopic and topic:
+
+    # we do not filter in the 1 case to allow prev to t0
+    if currenttopic and topic and _gettopicidx(p1) != 1:
         parents = [ctx for ctx in parents if ctx.topic() == currenttopic]
 
     # issue message for the various case
@@ -2067,7 +2077,11 @@
         target, bookmark = _findprevtarget(repo, displayer,
                                            opts.get('move_bookmark'), topic)
         if target is not None:
-            _prevupdate(repo, displayer, target, bookmark, dryrunopt)
+            overrides = {}
+            if topic and _getcurrenttopic(repo) != _gettopic(target):
+                overrides[('_internal', 'keep-topic')] = 'yes'
+            with repo.ui.configoverride(overrides, source='topic-extension'):
+                _prevupdate(repo, displayer, target, bookmark, dryrunopt)
             return 0
         else:
             return 1

--- a/tests/test-evolve-topic.t	Fri Jul 14 02:42:33 2017 +0200
+++ b/tests/test-evolve-topic.t	Fri Jul 14 02:46:28 2017 +0200
@@ -209,10 +209,14 @@
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
   [16] add ggg
   $ hg prev
+  preserving the current topic 'bar'
+  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  [15] add fff
+  $ hg prev
   no parent in topic "bar"
   (do you want --no-topic)
   [1]
   $ hg prev --no-topic
   switching to topic foo
   0 files updated, 0 files merged, 1 files removed, 0 files unresolved
-  [15] add fff
+  [14] add eee